[A/Z rights reserved.
„ IIA N D В О О К
w.o."
1373
OF THE
ME К ОМЕТЕ В.
1911.
v
LONDON:
PUBLISHED BY IIJS MAJESTY’S STATIONERY OFFICE.
To be purchased, cither directly or through any Bookseller, from
WYMAN AND SONS, Ltd., Fettkr Lank, E.C.; or
OLIVER AND BOYD, Twkkddale Court, Edinburgh; or
E. PONSONBY, Ltd., 116, Grafton Strkkt, Dublin.
PRINTED BY
MACKIE AND CO. Ltd., Warrington and London.
Price Sir pence.
CONTENTS.
PAGE,
Chapter I.		Description of the instrument	1
Я	IT.	Method of carrying the equipment		6
я	ИТ.	Range-taking			7
я	IV.	Theory of the instrument		15
я	V.	Errors of manipulation and their results		20
я	VI.	Miscellaneous ..	24
я	VII.	Instructions for testing the mekometer by regimental officers 	 	 and Instructions for testing and adjusting mekometers by	28
		qualified officers	 PLATES.	30
Plate	I. 1	The right angle instrument		4
я	и.	The reading instrument			5
я	III.	Method of holding the mekometer (standing)	9
я	IV.	я	я	я	(kneeling)	10
я	V.	я	я	я	(lying)	10
н	VI.	я	я	я	(sitting)	10
я	VII.	Right angle man, following a moving target	12
HANDBOOK OF THE MEKOMETER.
CHAPTER I.
DESCRIPTION OF THE INSTRUMENT.
A set of mekometers, as issued to a battery of horse, field, or
mountain artillery, consists ot (rule “ List of Changes,” §§ 9011 -2).
Two instruments of brass, one “ Right ” and one “ Left.”
Two reels ot aluminium with cords.
Accessories for each Instrument.—Handle; two telescopes; case
complete. For horse artillery only ; one belt, leather, waist, brown,
pistol, for each instrument.
The equipment of a battery of horse or field artillery consists
of one set ot instruments complete.
A set of mekometers, as issued to a battalion of infantry, con-
sists of (rule “List of Changes,” § 8927).
Two instruments of aluminium, one “ Right,” one “Lett.”
Two reels of aluminium with cords.
Accessories for each Instrument.—Handle, telescope, case com-
plete.
As the artillery and infantry mekometers vary only in structural
details, a full description of the artillery instrument only is given,
the points ot variation between the two being noted as they occur.
The instruments are closed boxes of brass (infantry, of
aluminium), with sliding covers of the same, secured in position by
a screw at the rear end.
The reading instrument is the larger. The measurements are
as follows :—
AirriTJiERY Instrument.
Heading Instrument.—Length, 4g- inches; breadth, 2J inches;
depth, 1$ inches.
Hight Angle Instrument.—Length, 3g inches ; breadth,
2J inches; depth, 1^ inches.
Infantry Instrument.
Heading Instrument.—Length, 4g inches; breadth, 2J inches;
depth, 1A inches.
Hight Angle Instillment.—Length, 3g inches; breadth,
2J inches; depth, inches.
The weights arc as follows :—
Artillery—
Reading instrument, complete in case,	about	...	3 lb.	IJoz.
Right angle instrument „	,,	...	2	,,	7 ,,
Reel, complete, with one cord, about	...	...	1	,,	12J ,,
p it
(2309) Wt 18114—395 20мг. 10/11 МЛСо. f -
2
* Mountain Artillery—
Both instruments are the same weight as the
artillery instruments; and the reel the same
weight as the infantry reel, Mark II.
Infantry—
Reading instrument, complete in case, about ... lib. 15ioz.
Right angle instrument . ,,	„	... 1„ 6 „
Reel, Mark I, complete, with one cord, about ... 0 ,, 14| ,,
Reel, Mark II, complete, with one cord, about ... 1 ,, 3£ „
General Service Micrometer.
This has been introduced into the Service (§ 12050, “List of
Changes ”) for all arms, and will supersede all other patterns
as they become unserviceable.
It differs from mekometers, hitherto described, in the following
main points:—
(1)	The instruments and reels are made of aluminium alloy.
The blocks on the back of the latter being in one casting with the
bottom disc.
(2)	The instruments are of the following dimensions
Heading Instrument.—Length, 4| inches; breadth, 2:| inches;
depth, lJ-£ inches.
Right Angle Instrument.—Length, 3} inches; breadth, 2]
inches; depth, 1~ inches.
The weights are as follows :—
Reading instrument, complete in case, about ... 3 lb. 0 oz.
Right angle instrument „	,,	2 ,, 5 ,,
Reel, with one cord, about ....................1	,, 9 ,,
(3)	The reading instrument is graduated for use with a
25 yard base. The drum is graduated from 500 to 6,000 yards.
. (4) Both the high and low power telescopes have a larger field
of view. The screw focussing arrangement of the eyepiece allows
of the correct focus being more rapidly obtained.
The Right Angle Instrument.
(Plate I.)
This has in it five openings:—(1) A circular one in rear, into
which the telescope fits by means of a socket; this can be closed
by a sliding shutter. (2) An opening on the right side, through
which the vane of the reading instrument is reflected to the eye
of the observer. (3) A T-shaped opening in front, through which
the object, the range of which is required, is seen by direct vision.
(4) A small opening in front, in the left-hand top corner, to admit
of the spring, which steadies the vane when raised, passing on with
the cover. (5) Underneath the box is a round hole, with a gun-
metal bush, tapped with a screw thread to receive the handle of
the instrument. On the cover is a flap, which can be folded down
when not in use; this is called “the vane.” Underneath the lid is
a spring to steady the vane when raised, which is secured to the
cover by two screws.
Inside the case are two frames, each secured to the bottom by
three screws and clamping nuts. The rear frame, nearest the eye-
hole, supports a mirror, termed the “ index mirror,” winch is wholly
silvered. The front frame supports a sheet of glass, the lower half
of which is silvered and the upper half plain ; it is termed the
“horizon mirror.” These two mirrors are each perpendicular to the
bottom of the box, and inclined to each other at an angle of 45°.
They are secured in their places in the frames by means of two
springs in front, and two screws behind each mirron A strip of
metal screwed into the top of each frame, and projecting over the
top of each mirror, prevents any vertical movement.0 The bottoms
of the mirrors rest on two horizontal pins.
The telescope socket projects into the interior of the case about
inch, to afford a firm bold to the telescope.
The sliding shutter is prevented from falling out of the grooved
'strips of metal in which it moves by stops on each side. The
shutter has a small eyehole drilled through it, for the purpose of
making rough observations.
Tile following marks will bo found on the top of the instrument
in front of the vane,
Mekr. Arty., II. & F. (or “G.S.” or “Infy.”)
Maker's name.
Year of supply.
In rear of the vane the number of the instrument, No. 228.
On the bottom of the drum Arty. II. & F. (G.S. or Infy.), and
lhe number of the instrument.
The number of the instrument is again registered on the
.bottom, and every separate part is stamped with it also.
The Reading Instrument.
(Plate II.)
This is a closed box, similar in shape to the right angle
instrument, but somewhat longer.
The openings in the box are identical with those in the right
angle instrument, except that the large opening in the side is on
the left, and there is an additional circular aperture on the right
side to admit the drum.
The interior of the box is strengthened by a metal rib on each
Bide, the infantry instrument having in addition an aluminium bar
screwed to the sides.
It contains the index and horizon mirrors, index arm, and
drum.
The drum is a brass cylinder, which has in it a steel-pointed
•screw shaft, working through a metal block, screwed to the bottom
of the box; the point of the shaft bears against a steel block on
the index arm.
* In the earlier made instrument» a strew with a large flat head, let into tho
top of the frame, was used instead of the metal strip.
4
The index arm and the frame of the index mirror are in one piece,
which is attached to the right side of the instrument by a German
silver spring, one end of the spring being screwed to a block
fastened to the side of the box, and the other to a block at the
back of the index mirror frame.
The index arm and mirror are thus free to follow the motion of
the screw shaft of the drum, the spring of the index arm always
keeping the arm bearing against the point of the screw shaft.
The horizon mirror is a fixture, as in the right angle instru-
ment ; but is raised off the bottom of the box, to allow the index
arm to work underneath it.
The index and horizon mirrors are similar in construction to
those previously described in the right angle instrument, and are
fixed in their frames in the same manner.
A small brass reader, with a line down the centre of it, projects
from the box above the drum aperture.
The other details of the reading instrument are identical with
those of the right angle instrument.
The exterior marks are the same; the number of the instru-
ment is also engraved on the end of the drum.
The Drum Graduations.
The drum has engraved on it spirally a scale of ranges,
calculated to read yards when the normal base is used (z.r., 50
yards with the artillery instrument, and 25 yards with the G.S.
and infantry instrument and the artillery instrument for mountain
artillery). The graduations read from right to left, and commence
at 500 in the artillery and G.S., and 800 in the infantry and
mountain artillery instruments respectively; they end at 5,000 in
artillery and infantry instruments, and at 6,000 in the G.S.
Beyond the 5,000 there is an arrow-head engraved on the
drum; when this is set opposite the mark on the reader, the index
mirror is set at an angle of 45° to the horizon mirror ; this is called
setting the drum at the Infinity Point.
For obtaining ranges of over 5,000 yards for Infantry and
Artillery Mekometers, or 6,000 for G.S. Mekometers, ясе instructions
in Chapter III. Ranges can thus be read to 10,000 yards with
Infantry and Artillery and 12,000 with G.S. Mekometers.
The Vane.
This is of gun-metal, and is painted black. The left side of it
in the reading instrument, and the right in the right angle instru-
ment is corrugated, and has a vertical strip of ivory down the
middle, secured to it by two screws. When not in use it folds down
flat on the top of the instrument, and is turned up at right angles
to the latter before making an observation. It should always be
turned down as soon as the operation of taking a range is finished.
Telescopes.
Two telescopes, one short and one long, are issued with each
reading and right angle instrument of the artillery and G.S.
Mekometer. Only the short telescope is issued with the Infantry
ТоГамра^е t
Plate 1.
Side, eLevaiiorb оГ lid/ with van# raised.
Right Angle/ InsLnjunenl/ (Plan •» arAucd size.)
А.А..Лол.
В....Shutter.
C. .. Telescope, socket.
D...Handle.....do.
E.E..Frames.
EF.F. . Adjusting screws.
G.G.G..Redlining spring.
H.H........do....projections.
K......Indecc mirror.
L......Horizon чгиггог.
/00. f8H<l/393. 20000. 9JI.
MeJby&Son*,Lith.
ню /в"4/з95. 20000.5. и.	М*1 bw4Sons.Uth
READING INSTRUMENT, INFANTRY.
(PloJb, clcIjajoL SVZ&.)
A I ................... "f
A. A...Возе
В......Shutter.
С......Telescope socket,
D......IruLejc arm.
E.E....Frames.
EEE....Adjusting screws.
H.H........do....projections.
K.„....Drum,.
L......German silver spring.
M......Index mirror.
N......Horizon mirror.
To facfi. роде.
Sh
5
Mekometer. The magnifying power of tho long toloscopo is about,
6 to 1, and of the short about 2 to 1. Tho latter will be found of
nso when a large field of view is required.
There are two glasses in each telescope ; the front one is termed
“ the object glass,” and consists in tho smaller of one, and in tho
larger of two lenses. The second, termed “ the eye lens,” is secured
in the eye-piece. This latter screws into tho tube of the telescope
by means of a screw thread of gradual pitch, and by means of this
screw the eye lens is focussed.
In the earlier infantry instruments tho oyopieco does not
screw, but fits into the tube, tho focussing being done by pushing
the eyepiece in or out.
The small telescope is secured to tho handle of tho mekometer
by a short piece of cord, tho largo telescope being carried in tho
case.
When inserting tho telescope into the socket of the instrument,
no force should bo used, but it should be pushed homo by a screwing
motion quite up to the shoulder.
Telescopes, except those of G.S. Mokomoters, are marked with
the number of the instrument with which they were issued, but all
Telescopes for Artillery and Infantry Mekometers are inter-
changeable. The Telescopes of G.S. Mekometers aro interchange-
able amongst themselves, but not with those of other patterns,
being rather larger.
The G.!S. Mekometer Telescopes aro engraved with tho word
“ High ” or “ Low ” to indicate tho power, and have an arrow
marked on them. In inserting tho telescope in tho mekometer
this arrow should bo brought opposite the arrow marked on the body
of tho mekometer.
The Handles.
Those are of wood, attached to tho small telescopes by a cord
about 4 inches long, with a gun-metal head to screw into the
socket in tho bottom of tho instrument. Beneath tho threaded por-
tion of the metal head is a recess, in which revolves a metal ring.
To this is attached a metal loop, to receive tho “ S ” hook of tho
base cord. Through a holo in the handle is fastened a cord lanyard,
intended to bo passed by tho operator over his wrist while using tho
instrument.
All handles aro interchangeable, but those of Artillery and
Infantry Mekometers aro marked with tho number of tho instru-
ment, and ф.
The Heel.
This is of aluminium. It is fitted internally with a brass
spring brake to prevent tho cord over-running itself when being
run out. It consists of two cheeks and a barrel, tho whole secured
together by a spindle running through the centre of the barrel and
clamped by a thumbscrew bearing on tho shoulder of the spindle
and screwed on to tho spindle. At tho back of tho reel is a flat
spring to enable it to be slipped on to tho rango-takor’s waist-bolt,
and a strap which is passed up behind this spring and the waist-belt
and passed through a small staple, then buttoned to a stud at the
top in order to secure the reel to tho belt.
6
The infantry reel is similar to the artillery reel, but of smaller
diameter.
All reels, artillery and infantry, have secured to them an
arrangement of leather straps, which buttons round the cord when
reeled up and prevents it getting loose, also a strap for securing
the reel to the belt.
The artillery reel takes a 50 yard cord ; the infantry a 25 yard
one.
Each reel is stamped with the maker’s name, ф , and year of
supply.
The Conn.
These are issued in lengths of 50 yards for the horse and iield
artillery, and 25 yards for the infantry, mountain artillery and
G.S. instruments. A reel holds one length. Each length has at
each end of it a brass hook, and the 25 yards cord has a small cord
loop in the centre—i.e., at 12| yards from either end.
The cord is made of hemp, covered with silk, and dressed with
a preparation of paraffin wax.
The Leather Cases.
These fit on the waist-belt by means of a strap and stud.
They are divided internally into compartments to receive the
different parts of the instrument, and are so arranged that the
most vulnerable parts of the latter are to the middle of the case.
Before putting instruments into their cases the drum should
he screwed to infinity point and the vane turned down.
The cases for each pattern of mekometer are of two sizes, that
for the reading instrument being larger than that for the right
angle instrument. Each is secured by a strap and a buckle.
Each is stamped on the back loop with the nature and number
of the instrument, and /f» on top of lid.
The cases of the artillery and G.S. mekometers are fitted with
a shoulder-strap (vide List of Changes, § 8711).
Chapter II.
METHOD OF CARRYING THE EQUIPMENT.
A.	By a Mounted Party.
A mounted range-taking party consists of No. 1, the reading
man ; No. 2, the right-angle man; No. 8, the horse-holder.
The equipment is carried by Nos. 1 and 2 as follows:—
No. 1 carries the reading instrument, in its case, on his belt
on tho left side, and a reel with 50 yards of cord on the right.
No. 2 carries the right-angle instrument and reel in the same
way as No. 1. .
Formation.
The party ride in line, No. 1 on the off side, No. 2 on the near
side of the horse-holder.
7
Dismounting.
At the command from No. 1 “ Malt—Dismount,” both numbers
dismount, No. 1 on the off side, and give their horses to the horse-
holder. They then proceed to the front on foot, and the horse-
holder takes the horses under cover according to directions
from No. 1.
Mounting.
At a signal from No. 1 the horse-holder brings up the horses,
that of No. 1 on the off, that of No. 2 on the near side.
The range-takers mount together.
B.	An Infantby Party.
An infantry range-taking party consists of No. 1, the reading
man, and No. 2, the right angle man.
The equipment is carried by Nos. 1 and 2 as follows:—
No. 1 carries tho reading instrument, in its case, on his belt
on the right side, and a reel with 25 yards of cord on the left.
No. 2 carries the right angle instrument, in its case, on his
belt on the left side, and reel with 25 yards of cord on the right.
Chapter III.
RANGE-TAKING.
General Instructions.
The following instructions will be observed whenever ranges
.•are being taken with the mekometer, in order to habituate men to
tho correct methods :—
(1)	Rapidity and scrupulous accuracy are essential to successful
range-taking. These are only attained by progressive and careful
training, which must ensure that accuracy is never sacrificed to
rapidity, while the latter is gradually obtained as proficiency
increases.
(2)	Great importance must be attached to previous consulta-
tion to ensure that not only the object, but also the exact part of it
upon which it is decided to take the range, is clearly understood by
both numbers before they separate. While the base is being
«extended, the object should be kept in view, ride Figure 12,
Chapter V.
(8)	Every advantage must be taken of ground and cover to
•conceal the movement and actions of the range-takers. Sky lines
must be avoided.
(1)	When it can be avoided, ranges should not be taken from
the actual position which it is intended to occupy with troops, so as
not to disclose it, should the enemy detect the presence of the
range-takers.
(5)	The range-takers will adopt positions which offer the
greatest steadiness, while affording the best concealment, having
•due regard to ground and available cover. The maximum steadi-
ness is obtained when both elbows can be rested, and this indicates
the adoption of the prone position whenever possible.
8
(6)	When it is necessary to call out instructions after the base
has been extended, the man spoken to should invariably repeat the
instructions given.
(7)	When obviously wrong readings are being registered, or
the drum runs out before a coincidence has been obtained, both
numbers should unhook the cord and meet for further consulta-
tion.
(8)	Instruments should never be left on the ground.
(9)	The right angle must always be got roughly without the
telescope, but the telescope will invariably be used to obtain
coincidence.
(10)	The range should be given as the mean of three readings*
Should one reading differ considerably from the other two,
another should be taken, and the incorrect reading disregarded.
After each reading, the drum should invariably be turned off
counter-clockwise (i.e., to read a shorter range).
(11)	It is generally advisable for only one number to extend
the base while the other remains stationary. This must, however,
depend upon the nature of the ground. In any case the direction
in which the base is to be extended should be decided during
consultation, as bushes, etc., may interfere with the cord should
subsequent forward or backward movement be found necessary.
(12)	For ranges over 2,000 yards with the Infantry, 5,000 yards
with the Artillery, and 6,000 yards with the General Service
Mekometer, a double base must always be used if the ground
permits; the reading of the drum must then be doubled.
Cases may arise when it is convenient to use a half base (25
or 12J yards), but this should not be dpne if it can be avoided.
When using the Artillery reel the 25 yard base will be obtained
by doubling the 50 yard cord and passing the handle of the reading
instrument through the bight thus formed, both ends of the cord
being attached to the left instrument.
With the Infantry reel the 12J yard base will be obtained by
slipping the handle of the right angle instrument through the loop
in the centre of the cord.
When the half base is used the range registered by the drum
must be halved.
(13)	Like all mechanical instruments, the mekometer must be
tested from time to time to ensure that it is in correct adjustment*
It must be kept thoroughly clean, and treated with care. A
mekometer in adjustment and properly looked after is a thoroughly
reliable and valuable instrument in the hands of well-trained men ;
otherwise, it is worse than useless.
2. Taking a Range.
Instruction should be progressive and divided into two stages,
viz.: (a) Elementary and (6) Advanced. It is essential that every
detail of the elementary stage should be thoroughly known before
the advanced stage is begun.
Short lectures, explanatory of, and corresponding to, the stage
of practical instruction reached, should be given from time to time*
These should include the object and method of ranging with the
Mekometer, use of range charts and key ranges, the necessity for
Т, •</ .'.ш/
411 tLLV'M
9
accuracy and rapidity, the importance of concealment, the theory
of the instrument, errors in manipulation and their results, care
and cleaning of instruments.
(a)	Elementary Stage.
It is important that tho same sequence of instruction should
be followed as is actually adopted when taking a range under
service conditions. By this means, correct habit is acquired, and
minor details arc not overlooked.
(1)	Preparation oj instruments and reels.—Tho instruments are
taken out of their cases and handles attached. Telescopes are
focussed; this is important, and should be carefully taught, with
practice but little time should be required for this. The necessity
for using the telescope when obtaining coincidence should bo
emphasised, as there is often a tendency not to use it, which
renders the coincidence less accurate.
The strap covers of the reels are unbuttoned and tucked back
under the belt, so as not to obstruct the free run of tho cord.
(2)	Extending the base eord.—This should be practised first
with the single and then with the double base. Various methods
should also be practised, viz., No. 1 remaining stationary while
No. 2 doubles out; No. 2 stationary while No. 1 doubles out; and
Nos. 1 and 2 doubling outwards from the centre. Tho rangotakers
will decide after consultation the direction in which the base is to
be extended. This will always bo carried out with reference to a
given object to which it is supposed the range is required. Range”
takers must be taught to extend the base approximately at right
angles to an imaginary line from the position that will be occupied
by No. 2, to the object. By this means the necessity for forward
and backward movement after the base is extended, will be mini-
mised. This is an important consideration when range taking
under service conditions, for difficulty will often bo experienced if
obstructions such as buslies, etc., have to be cleared when obtaining
the right angle.
The method of extending tho base will bo as follows :—
For a single, base.—No. 1 takes a turn of No. 2’s cord round
his loft hand. Then either, or both, numbers double
out in tho direction fixed upon, the cord being allowed
to run freely on the reel.
For the double base.—No. 1 hooks the two cords together;
the procedure is then as for a single base.
While extending the base, tho object must be kept in view to*
ensure that its position is not lost, or that it is not obscured by an
intervening obstruction. On arriving at the full length of the cord,
Nos. 1 and 2 hook their respective ends of the cord on to tho metal
loop on the handle of the instruments and raise tho vanes.
(3)	Method oj holding the. instruments.—No. 1 holds the handle
with three lingers of the left hand, while, with the thumb and fore-
finger, he steadies the instrument (Plato III, Figure 2). His right
hand is on tho drum ready to make his coincidence. No. 2 holds
tho instrument with both hands, the three lingers of tho right hand
10
holding the handle, while the forefinger and thumb steady the in-
strument on the right side; the three fingers of the left hand
pressing on those of the right hand, while the forefinger and thumb
steady the instrument on the left side (Plate III, Figure 1).
Whenever possible, the elbows should be rested, and for this
reason the prone and sitting positions are the steadiest, unless a
suitable object is available, such as a wall, tree stump, etc., when
the kneeling or standing position may be preferable. (Plates IV,
V and VI.)
Practice should be afforded in range taking in all positions
with and without the elbows rested.
(4)	Heading the drum,—The graduations are described in
Chapter I. It is most important that these graduations should be
thoroughly understood, and that range-takers should be able to
read the drum quickly and accurately before ranges are actually
taken. At all instructional exercises, the range-taker should be
required to state the reading, and the instructor should invariably
check the reading by examining the drum.
(5)	Obtaining the right angle,—As soon as he has hooked the end
of the cord on to his instrument and raised the vane, No. 1 assumes
a steady position (lying, sitting, etc.), and revolves the drum to
his estimate of the range. He then aligns his instrument on the
object and remains steady.
No. 2, having hooked his end of the cord to his instrument and
raised the vane, takes out the telescope and moves backwards or
forwards as required until he sees the vane of No. I’s instrument
approximately on the object; the right angle has then been roughly
obtained. If the reflection of No. Гв vane appears to the right of
the object, he must retire ; if to the left, he must advance. The
.short rule is:—Bight—retire. Left—advance.
The cord must be kept taut; this is primarily the duty of
No. 2 but No. 1 must also assist. It is of great importance that the
right angle should be obtained approximately, with rapidity and
reasonable accuracy in order to reduce movement to a minimum
after the base has been extended. As proficiency increases it may
often be advantageous to obtain the right angle with the telescope
adjusted.
(6)	Obtaining coincidence,—Correct range-taking depends
primarily upon the accuracy of the coincidence. As soon as No. 2
has obtained the approximate right angle he replaces the telescope
in the instrument, and looking through it at the object, finally
adjusts the right angle by a slight forward or backward movement
until the reflection of the white strip on No. l’s vane is seen over-
lying the exact part of the object previously agreed upon between
the range-takers. The correct coincidence and therefore an accurate
right angle has then been obtained.
Having obtained a coincidence, No. 2 calls out “ On” in a
long-drawn singing tone, the object being to prevent the jerk which
would result from a sharp call, and would make him lose the
coincidence momentarily. He then remains steady until he sees
(by reflection) that No. 1 has taken down his instrument to read
the range. No. 2 must retain his position, keeping the instrument
to his eye, in order to get coincidence again as soon as No. 1 is
ready.
PLATE IV.
T« face /I. 10.
PLATE V.
To face р. 10.
PLATE VI.
To for-' p. 10.
J
11
Meanwhile No. 1, by turning the drum, brings tho reflection
of the white strip on No. 2’s vane slightly to the left of tho object
and keeps it there while No. 2 is getting coincidence, and us
soon as No. 2 calls “ On,” No. 1 makes the final adjustment by
slightly turning the drum away from him until accurate coincidence
is effected. Ho then lowers the instrument and reads the range on
the drum.
Both range-takers must be careful to keep tho object in tho
centre of the field of tho telescope (or in the centre of the “[“-shaped
opening, if a telescope is not used).
So important is accuracy of coincidence that the instrument,
should, if possible, be fixed on rests (a barrack room form or table
is suitable), so that men can bo shown practically what is a correct
coincidence.
(7)	When some proficiency has been attained in tho above
details, ranges should be taken. In this stage, all ranges should bo
to easy objects, and the ground from which the ranges are taken
should afford no difficulties. All positions should be practised,
viz., lying, sitting, kneeling, and standing—in tho two last, both
with and without rests for the arms.
It must not be overlooked that correct methods of detail and
scrupulous accuracy are to be made habitual in this stage, and
therefore, until these have been attained, tho advanced stage should
not be begun.
(6)	Advanced Stage.
In this stage the conditions and requirements of active service
will be assimilated. Rapidity in range-taking must be increased
until at least the standard time of two minutes is reached (Musketry
Regulations).
Care and practice is necessary to ensure that rapidity combined
with accuracy is constantly maintained. Instruction must be
afforded in various natures of ground, special attention being paid
to concealment in consultation and movement.
Positions must bo adopted which are suitable to tho ground
and cover available.0
Practice should be afforded in taking ranges beyond 1,100
yards because the inekometer will seldom be used on service within
this distance.
Objects selected for range-taking will be chosen so that they
become progressively more diflicult, and approximate more nearly
to service conditions. A practical method is to select an object
upon which it is possible to take the range with the mekometer, lay
a rifle from an aiming rest upon a possible fire position in the-
vicinity of the object selected, then tell the range-takers that the
range is required to the fire position upon which the rifle is laid,
but without referring to the object selected. The range-takers
having looked along tho rifle, will be required to obtain the range
to the position indicated. On service, an enemy will generally
avoid the vicinity of good ranging marks, and therefore range
takers must be afforded practice in taking the range upon objects
not actually at the position to which the range is required. Con-
* If a high wind is blowing, making it diflicult to hold tho instrument steady, owing
to the vibration of the cord, it will bo found advantageous to unhook the cord from
the instrument, and attach it to the waist belt instead, shortening the cord Bufllciently
to allow for the distance of the instrument from tho point to which tho cord is attached..
12
siderable practice is necessary, particularly in undulating country,
to recognize when an object to which the range is taken is not
actually on the same feature as the position to which the range is
required. When such an object is selected, as being the only one
available, this must be reported to the officer to whom the range is
given.
The preparation of range charts, particularly for defensive
positions, and taking ranges to prominent objects to serve as key
ranges in the attack, must be practised.
Range-Taking to Moving Objects.
All Artillery range-takers, and only those in Infantry and
Cavalry who obtain 85 marks in the tests laid down in Musketry
Regulations, will receive instruction in range-taking to moving
objects.
The mekometer is admirably adapted for taking ranges to
moving objects, and was introduced principally for this purpose.
The procedure is precisely the same as in range-taking to a
stationary object, but the right angle man has to follow up the
target as it moves.
A.	When the object is moving across the front from left to
right.
We will suppose for the sake of illustration that the target is a
single mounted man, in which case the coincidence should be made
on the man’s body and the strip of ivory on the vane cover it.
No. 2 having got a rough right angle in front of the target,
settles himself well back with his left foot well in advance, weight
of his body on his right leg, both legs somewhat bent (see Fig. 1,
Plate VII). He then looks through. his instrument, with the
telescope in, and gradually meets the object as it moves forward.
As soon as he effects coincidence he calls “On,” and follows the target
up with the reflection of No. l’s vane, coming gradually forward, first
to an upright position (see Fig. 2, Plate VII), and then into one
leaning forward with the weight of his body on the left leg (see
Fig. 3, Plate VII). He should endeavour to keep the coincidence
perfect sufficiently long to enable No. 1 to effect his coincidence.
As soon as No. 1 lowers his instrument to read the range, No. 2
takes a pace forward and gets into the backward position, ready to
right angle No. 1 on to the object again.
No. 1 should get the reflection of No. 2*s vane slightly in front
-of the object, and, as the latter passes the vane, follow it up slightly
by turning the drum from him, effect coincidence again and read
the range.
B.	When the object is moving across the front from right to
left.
No. 2 gets into the forward position, allows the object to meet
the reflection of No. l’s vane, and calling “ On” follows it up till
he gets into the backward position.
No. 1 gets the reflection of No. 2’s vane somewhat in front of,
z.e., to the left of the object, and meets the latter as it moves by
turning the drum from him. Directly he has effected coincidence
he reads the range.
C.	When the object is moving directly away from the observer.
No. 2 in this case has not to move; No. 1 proceeds as in A.
D. When the object is moving directly towards the observer.
PLATE VII.
To face p. 12.
Fig. 2	Fig. 3.
13
No. 2 lias not to move; No. 1 proceeds as in 13.
The range-taking to moving objects which will bo found the
hardest and require the most practice is Case В; the more nearly
the object’s movement approaches a perpendicular to the observers
the easier the operations become.
In range-taking on moving objects the drum should not be
turned off after each observation.
Smart range-takers in good practice should easily be able to
take live or six observations per minute on moving objects.
The regularity of the increase or decrease of the successive
ranges will be a guide to No. 1 as to the correctness of the work
being done by himself and No. 2.
A few hints as to what to observe in moving bodies of troops
may be useful, and are therefore collected here.
The great desiderata, from a range-taker’s point of view, in an
individual selected to be observed in a body of troops are that his
pace should be the mean pace of the whole body, that he docs not
shift his position in the body of which ho forms part, and that ho is
not easily lost in the body as it moves. A General and his Staff
would bo the worst of objects to observe, as the members composing
it arc constantly shifting their places among themselves; so, again,
a mounted officer of any arm may be expected to shift his place anil
to disappear and reappear among his men. It will, therefore, as a
general rule, be found best to select the man on the nearest Hank of
the leading fours or section, and with artillery the lead driver of
the leading gun.
A Method of Теасшхи the Elementary Use of the Mekometer
in Drill Halls or. Confined Spaces. •
(1) This method is useful when opportunities for practice in
open country are limited. It enables elementary instruction to be
afforded, and such matters as accurate coincidence, reading of the
drum, etc., can be taught and practised. This method cannot
replace, but is merely to be considered as jjreparatory to instruction
and practice in the open.
(2) The principle of the method is that the rays, instead of
meeting at a distant object, are, as it were, intercepted at a short
distance from the observers by duplicate representations of the
same object placed in front of each observer. Two similar
landscape targets are very suitable.
(8) Method of carrifuuj out.—Place two similar landscape
targets in line, and at a distance apart which is proportional to the
base being used, measuring from the same object on both land-
scapes, e.i/., with a 25 yards base, between 24 and 25 yards apart;
with a 12j yards base, between 12 and 12J yards apart.
The reading man places himself at a rough perpendicular to
the target, and at a distance of not less than 7 yards from it.
The coincidence is then made in the usual manner, the range-
takers making coincidence on the same object on the target
opposite each, and the reading obtained should then be checked by
expert range-takers if available.
When checking a rending, care should be taken that the
reading instrument is held in the exact position used by the range-
taker under instruction.
14
The distance from the targets from which the range is taken
should be as great as the space available will permit, since
differences in readings due to slight alterations of position will
thereby be minimised, while at the same time the instruction is of
a more practical nature.
(4) The positions or objects to which ranges are required can
be indicated either by word of mouth or by laying a rifle on to a.
fire position or point.
Inaccurate Instruments.
If an instrument is not reading accurately, and it is not
possible to have it adjusted immediately, it can sometimes be
made temporarily serviceable as described below. Inaccurate
instruments should, however, be adjusted as soon as possible, as
laid down on page 30 et scq.
In the very large majority of cases the inaccuracy has been
caused through some jar (owing to the instrument being dropped),
causing one of the mirrors to be slightly shifted from its proper
position. The jar has not, however, been sufficient to loosen the
mirror, and tho mirror will consequently remain in its new
position. In this case an accurate reading can be taken by the
following procedure:—
Test the instrument at 800 yards, and we will suppose it reads
880 yards for 800 yards. At the point on the box of the reading
instrument opposite 800 yards (which is the reading that should
have been obtained) make a small mark with a knife or a pencil.
Then test the instrument at say 1,200 yards, and instead of
reading the drum from the original line on the projecting brass strip,
read it from the new mark made on the box with the knife, using
tho brass strip only to indicate on which spiral ring to read, ед/.—
Ф11'1 и
llUIUMM—l
I
wiiiiiiiiiiiiiiiiiHiiiiiiiiiii]
In the above diagram the strip indicates ring B, as the correct
ring to read from, the actual point on ring В being indicated by
the new line made.
A.—Brass strip.
X.—Now line.
If then the reading obtained comes within the percentage of
error allowed, viz., at 1,200 yards 2‘4% of the range, or between
1,170 and 1,230 yards, the instrument will give accurate readings
when read from the new line.	0
15
It is necessary to test the instrument at 2 ranges to ascertain
if the error is constant and not varying, which would be the case if
the inaccurately set mirror was loose.
CiiAirmt IV.
THEORY OF THE INSTRUMENT.
The Mirrors.
Theorem.— If a ray of light sillier double reduction, the angle
between the original ray and its direction after the second reflection
is double the angle made by the reflecting surfaces.
Suppose that in the right angle instrument coincidence of the
object and the vane of the reading instrument has been effected.
Fin. 1.
Let E (Fig. 1) be the eye looking through the unsilvered part
of the horizon glass E at the object O. Let A be the vane of the
reading instrument, the reflection of which falls first on the index
glass xV at the angle 6, and from it passes off at the angle //, and
falls upon the horizon glass (silvered portion) at the angle c, being
reflected thence to the eye at the angle c. Let d be the angle of
inclination of the mirrors to each other, and a the angle between
the ray from О to the eye and that from Л to Лг.
We know by optics that—
The angle of incidence ~ the angle of reflection..........(1);
and by Euclid that—
The exterior angle of any triangle ~ the two interior
and opposite angles.......................................(2).
By (1)	b =- //,
r — c'.
18111
В
16
By (2)	с'+PFN = d+b'=d+b,
and	b+FNP = d+c = d+c'.
Adding	b+c' +FNP + PFN = 2d+5+c'.
That is	FNP + PFN = 2d.
But the angle a = FNP + PFN hy (2).
Therefore	a = 2d.
If then	d = 45°,	a = 90°.
The Range-finding Triangle.
The principal application of the mekometer is to solve without
calculation or actual measurement the following problem:—
To find the distance to a visible point from the ground
occupied by the operator.
This is termed “ Taking the Range.”
The conditions necessary in order to take a range with the
mekometer from a point P to an object О (Fig. 2) are that a position,
Q, may be found to the left of P at the normal length of the base
(25 or 50 yards) such that the three points О, P, Q are all visible
one from the other, and that the angle OQP is a right angle.
Fig. 2.
To solve such a triangle, we require to know the base QP and
the measure of the angle POQ, the angle OQP being always a right
angle. We are unable, however, to get at the point О to measure
the angle, and therefore must find a line, PI), at right angles to PQ
and measure the angle OPT), which is equal to the angle POQ.
This is done in taking the range with the reading instrument.
17
When the drum is set at the infinity point (tho mirrors being
then inclined to each other at an angle of 45°), tho vane of the
right angle instrument Q will bo seen reflected in the direction 7),
at right angles to PQ. By turning tho drum towards you, tho
imago is made to move to the left, and can be brought to coincide
with the object O. The inclination of tho mirrors is a measure of
the angle OPP or POQ.
The drum is so graduated that for any given angle, OPP,
through which the image of the vane of tho right angle instrument
is made to travel tho distance QO is registered thereon in yards
when using a normal base.
The Fixing of the Bight Angle.
When No. 2 has extended his half of tho base as described in
Chapter III, ho looks through his instrument and will, as he has
not yet established a correct right angle, see P tho vane of the
reading instrument reflected to the right or left of the object O.
Assuming that ho sees it to tho right of О as at P", then OQaP is
manifestly greater than a right angle, and ho must retire to a point
Q such that from thence the reflection of P will coincide with 0.
Mee Figs. 8 and 4.
Fig. 3.
18
Fig 4.
Fig. 5.
If, on the other hand, tho reflection of P appears to the left of
О as at Pb, the angle OQbP is less than a right angle, and No. 2
must advance to Q. See Figs. 3 and 5.
Hence the short rule given above at page 10,“ Left, Advance—
Right, Retire.”
Taking the Range.
No. 2 having established the right angle, when No. 1 looks
through his instrument, with the drum set at the infinity point, he
will see the reflection of No. 2’s vane Q in the silvered portion of tho
horizon glass in the direction Qft at right angles to the base QP and
to the right of the object 0 (Fig. G).
19
To obtain the reading of the range QO he must make the
reflection of Q coincide with 0. To do this he turns the drum
towards him, and the reflection of Q travels across the horizon glass
to Q1 (Figs. 6 and 7).
When the reflection of Q is exactly underneath that part of the
object previously agreed upon by Nos. 1 and 2 (in the figures the
vane on the church steeple), the drum registers the range from Q
to 0.
Eki. 6.
Ею. 7.
20
Chapter V.
ERRORS OF MANIPULATION AND THEIR RESULTS.
Errors made by the Right Angle Man or No. 2.
Assuming that No. 1 makes his coincidences correctly, suppose
that No. 2 makes his coincidence to the left of the proper object 0
(Fig. 8) at X. No. 2 is therefore in the position Q' instead of Q, and
consequently, the drum being at infinity point, No. 1 sees the
reflection of No. 2’s vane at Qb instead of at Qa. To effect his
coincidence he turns the reflection of No. 2’s vane through the
angle QbPO, instead of through the angle QaPO, and therefore
reads too high a range, i.e., he reads the range Q'Z instead of QO.
Fig. 8.	Fig. 9.
If, on the other hand, No. 2 makes his coincidence to the right of
tho proper object О (Fig. 9), he will cause No. 1 to read too low a
range, i.e., the distance Q'Z instead of QO.
Errors made by the Reading Man or No. 1.
Assuming that No. 2 makes his coincidences correctly, suppose
that No. 1 makes his coincidence to the right of the proper object 0
(Fig. 10) at No. 1 has therefore turned the reflection of No. 2’s
vane through the angle Qn PX instead of through the angle Q* PO
and the range recorded will consequently be too high, as it will be
the distance QZ instead of QO.
21
If, on the other hand, No. 1 makes his coincidence to the left
of the proper object 0 (Fig. 11), tho converse of tho above will be
the case.
Fig 11.
Fig. 10.
Nearly all the errors and absolute failures in range-finding are
due to one or other of tho above mistakes in observation, and it is
most essential to impress on learners what grave errors in the range
result from them. They originate, as a rule, from one of two
causes—
(1) Slipshod or hurried consultation between tho range-takers as
to the exact point of the object to be observed.
(2) Not watching the object as the base is extended.
As an example of (1) tho following is given. Two range-takers
arrange to take the range of the left gun of a battery in action, but
they neglect to settle what part of the gun they shall observe. After
extending the base, No. 2 right angles No. 1 on to tho muzzle of
the gun, but No. 1 makes his coincidence on tho right wheel, i.r.,
tho wheel to his right. Assuming that tho distance from No. 2 to
tho muzzle of tho gun is 2,000 yards, and that the distance from the
centre of tho muzzle of tho gun to the wheel is 1 yard, the range
road by No. 1 will be 2,041 yards nearly (if a 60 yards base is used).
The importance of watching the object as tho base is being
extended is apparent from Fig. 12. Tho rango-takors, when they
come up to /7, sec tho tree a4 to tho loft of. tho wood 1Г, and agree
to take tho range to it. They do not, however, watch the object as
22
they run out, and on reaching the limits of the base, No. 2 sees the
tree a5 to the left of 1И, and right angles No. 1 on to it, while No. 1
observes the tree a3. The result would obviously be much too short
a range.
Fig. 12.
Errors due to the Base Cord.
These may arise from two causes.
(1) The cord being the wrong length.
(2) The No. 2 not keeping the cord stretched when taking the
range.
It is obvious that too long a cord will cause too low a range to
be registered, and vice versa.
It is well to remember that:—
When working with a 25 yards base, an error of 9 inches in
the cord makes an error in the range of 1 per cent.
With a 50 yards base, an error of 18 inches does the same.
With a 100 yards base, an error of 36 inches does the same.
Note,—The cord is liable to shrink when wet. If, however, it
is wetted when on the reel, the shrinkage will not exceed 3 inches,
and may be neglected. If thoroughly soaked when unreeled, the
shrinkage may amount to as much as 1 foot.
23
NOTES ON CLEANING MIRRORS, TELESCOPES, AND
TELESCOPE TUBES OF MEKOMETERS.
To CLEAN THE MlRHORS.
Take a small piece of stick or lead pencil, about four inches
long, and tie a clean piece of chamois leather or soft rag round one end
to form a small knob. Put this end through the opening in the
side of the frame and clean each mirror, special care being taken
not to injure the silvered portion of the horizon mirror. Great care
niust be taken that the chamois leather or rag is quite free from
grease, and also that the mirrors are not rubbed too hard.
To CLEAN THE OBJECT (iLASH OF TJJE TELESCOPE.
Unscrew the object glass by turning it to the left, and clean both
sides of the glass with a clean piece of soft rag or chamois leather.
Holding the telescope in the left hand, object glass towards the
right hand, screw in the object glass by gently turning it to the
right, care being taken that it is in the correct thread, winch will be
known by its working smoothly. It should be screwed as tightly
home as can bo done with the lingers. The eye-piece of the
telescope seldom requires chaining, and it is not advisable to take it
to pieces. Lenses should never be removed from their cells.
Flap on Cover.
Should the Пар on the cover become too tight, put a few drops
of oil into the joint, and at each end of the spindle on which the Пар
turns. Work the Hap backwards and forwards until the oil has
found its way into the joint.
Fitting of Telescope in the Instrument.
The telescope may become tight in entering or withdrawing it
from its tube. It will be found to move in the tube quite easily
after being cleaned, provided the telescope or tube is not damaged.
For cleaning, take a piece of rag, put a few drops of paraffin oil
upon it, and rub the inside of the tube until dean. Do the same
with the part of the telescope which Hts into the tube.
General.
In any cleaning, great care must be taken not to allow any oil,
grease or paraffin to get upon the mirrors or telescope glasses.
Whenever the cord is broken, care must bo taken to make it up
to the correct length. A difference of nine inches in the length of
the twenty-live yards cord will make a difference of one per cent, in
the range, with that base.
Mekometurs should be inspected weekly to ensure that they are
kept clean and in good order.
24
Chapter VI.
MISCELLANEOUS.
To take Ranges with the Reading Instrument only.
There are two ways of doing this :—
Method I (Figure 13).
Fig. Ж
The drum is set at the infinity point. The observer faces the
object, and, looking through the instrument, moves backwards or
forwards (if the reflection is to the right of 0, he will advance; if
to the left, retire; the rule in this case being the converse of that
followed when fixing the right angle, since the glasses of the
reading instrument reflect to the left), till he obtains coincidence
between 0 and some clear distant object, X to his left. He marks
the point Q, where he is standing, and from that point extends his
base cord in the direction QP, taking care to have three points X,
Q, and P in one line. Standing at P, he will see the reflection of
X at Xa; then by turning the drum and effecting coincidence
between 0 and Xa, he will obtain the range of 0 from Q.
Method II (Figure 14).
The drum is set at the infinity point. The observer, standing at
Q with his left shoulder towards the object 0, looks through his
instrument and moves right or left till ho obtains a coincidence
between the reflection of 0 and some clear and distant object X.
He then marks the spot Q, and extends his base from Q to P,
keeping X, Q, and P in a straight line. Looking through his
instrument again in the direction PX, he will see the reflection of
25
0 to tho right of X, at Oft, and, by turning the drum to make the
reflection of О coincide with X, he obtain» the range (JO.
Pig. 14 is purposely drawn out of proportion in order to
emphasize the base PQ. The linos OP, OttP are at right angles to
each other when the drum is at the infinity point.
In the description above given of tho two methods, No. 1 is
snj)])osed to bo working entirely by himself; if, however, he has his
No. 2 with him ho can, if ho finds it convenient, send out the latter
to act as a distant point.
On the use of отпев» than the Nobmab Base.
It should, whenever possible, be made a rule:—
To use a base of 100 yards with tho artillery instrument for all
ranges over 5,000 yards.
To use a base of 50 yards with the infantry instrument for all
ranges over 2,000 yards.
It is obvious from the figure (Fig. 15), that a small lateral
error, made by the reading man at P, will cause a far larger error
in the measurement of the perpendicular QO, and, therefore, in the
range registered on the drum than the same lateral error will cause-
when the range is read from Pa, QP being equal to PP\
Cases may arise when it is convenient to use a half base (25
or 12 J yards) for a short range, but this should never bo done if it
can be avoided.
When using tho artillery reel, tho 25 yards base will be-
obtained by doubling the 50 yards cord, and passing tho handle of
the reading instrument through tho bight thus formed, and
attaching both hooks to tho right angle instrument.
With the infantry reel, the 12| yards base will bo obtained by
slipping tho handle of tho right angle instrument through the
centre loop of the cord, the hook being attached to the reading,
instrument.
26
With a double base the range registered by the drum must be
doubled, and with a half base must be halved.
Fig. 15.
Field Sketching.
The mekometer will be found very useful for executing rough
sketches or surveys of country.
To rapidly survey a position or plot of ground, take a Hat
board, or, preferably, a plane table, FGH, Fig. 16.
Fig. 16.
Select salient points, such as А, В, С, I), E, draw lines All,
1BH, etc., and take the ranges of AH, BH, etc., and mark these
distances on tho scale employed in the lines AH, BH, etc. As each
range ought not to take more than half a minute, a rapid and
.accurate survey can thus be made in a short time.
From the above it will be seen that the relative distances of
various points can be ascertained without occupying them.
Hedges, roads, &c., have in this way been plotted, and an
accurate survey made.
27
To find the Distance between two Inaccessible Points.
Fig. 17 shows how the distance between any two objects may
readily be determined.
Let SO bo any two points the distance between which it is-
required to ascertain. The ranges of S and 0 are taken from any
point Q, the right angle man remaining at the point (J during both
observations.
Lay out QA, QB in the same lines as QS, QO; make QA a.
convenient proportion of QS and QB the same proportion of QO.
Measure AB, which will bear the same ratio to OS.
Example:—
Lot QO -= 2,500 yards.
QS - 2,000 ’ „
Make QB -	- 25 yards.
QA - jyQ — 20	>(
Measure AB ; suppose it is 21 yards.
Then 21 x 100 -- 2,100 yards is tho distance between SO.
In practice, one man should pace the distance QB, and, having-
marked the point 13, should pace tho distance QA and then tha
distance AB.
On no account should No. 1 pace one lino and No. 2 tho other.
No two men pace alike.
To keep the exact line is very important. The length of the
pace is of no consequence, provided it is uniform. For greater
accuracy it is as well to pace the lines twice (once each way).
28
Calculation may be avoided thus :—
No. 1 when pacing QB, QA will take two paces for every
hundred yards, and then, when pacing AB, count a hundred yards
for every second pace, and so obtain AB at once in hundreds of
yards, an odd pace being 50 yards.
No. 2 should assist in keeping correct line. If No. 1 is pacing
towards О or S, he should stand at Q, and send No. 2 out towards
the point he intends to advance on, and rather beyond В or A.
Having carefully aligned him on the distant point, he then paces
directly towards him, halting and marking the spot when he has
gone the requisite number of paces. If No. 1 is, pacing away from
0 or S, he should stand at Q as before, but facing the other way,
and No. 2 should run out some distance and give him a point to
advance on, first of all taking care to align himself on No. 1 and
the distant point.
Chapteb VIL
INSTRUCTIONS FOR TESTING THE MEKOMETER BY
REGIMENTAL OFFICERS.
Artillery.
1.	See that all the parts of the mekometer are complete and in
good order; that the cords are of the correct lengths, and the reels
and cords are in serviceable condition.
2.	Ascertain the distance of some well-defined object between
1,500 and 2,000 yards, either by direct measurement (a rifle range
would probably give correctly measured distance), or, better still, by
careful triangulation.
3.	Take the range with 50-yard base six times, and divide the
range thus obtained by six to obtain the average reading.
4.	Work out the percentage of error of this reading and com-
pare with the following table:—
1,500 yards .......... 1*5	per cent.
1,600	„	  1*6
1,700	„	  1*7	„
1,800	„	  1*8	„
1,900	„	  1*9	„
2,000	„	  2*0	„
5.	Should the percentage of error exceed that given in tho
tables the instrument should be sent for adjustment to one of the
officers competent to adjust, if available in the Brigade. If not
available, the instrument should be returned for adjustment.
(See Regulations for Magazines, etc.)
Infantry.
1.	See that all the parts of the mekometer are complete and in
good order, that the cords are of the correct length, and the reels
and cords are in serviceable condition.
29
2.	Ascertain the distance of some well-defined object between
800 and 1,200 yards, either by direct measurement (a rille range
would probably give correctly measured distance), or, better still,
careful triangulation.
8.	Take the range with 25 yards base six times, and divide the
range thus obtained by six to obtain the average reading.
d. Work out the percentage of error of this reading, and com-
pare with the following table:—
800 yards ...	... I’G per cent
900	„	.......... 1’8	„
1,000	„	........ 2*0	„
1,100 ................2*2	„
1,200	„	........ 24	„
5. Should tho percentage of error exceed that given in the
tables the instrument should be sent for adjustment to one of tho
officers competent to adjust, if available in tho Brigade. If not
available, the instrument should be returned for adjustment. (See
Regulations for Magazines, Ac.)
Genehal Sbhvice.
1.	See that all the parts of the mekometer aro complete and in
good order, that tho cords aro of the correct length, and the reels
and cords are in serviceable condition.
2.	Ascertain the distances of as many well-defined objects as
possible between 1,000 yards and 4,000 yards, by careful triangu-
lation (a pocket sextant will do very well, or if possible use a
theodolite).
3.	Take the range with 25 yards base six times, and obtain tho
average reading.
•1. Work out the percentage of error of this reading, and
compare with the following table:—
1,000 yardH ...	... 1	per cent.
1,500 „	... 15	>>
2,000 „	... 2	
2,500 „	... 2-5	>>
3,000 „	... 3	ff
8,500 „	... 3-5	
•1,000 		... 1	
5,000 		... 5	
5. Should tho percentage of error exceed that given in the
tables the instrument should be sent for adjustment to one of tho
officers competent to adjust, if available in the brigade. If not
available, the instrument should be returned for adjustment (see.
Regulations for Magazines, Ac.).
G. Tho objects selected for testing purposes must bo well-
defined, such as a flagstaff for short and medium ranges, and a
church spire for longer ranges.
Note.—Tho officers qualified to adjust Mekometers are:—
(1)	Those who have qualified in
(a)	The Gunnery Staff Course.
(b)	Ordnance Course.
(2)	Inspectors of Ordnance Machinery.
(8)	Officers specially trained for this work.
30
INSTRUCTIONS FOR TESTING AND ADJUSTING
MEKOMETERS BY QUALIFIED OFFICERS.
I.—General Principles.
Mekometers, like other delicate instruments, are liable to get out
of adjustment. This is especially the case with the right instruments.
When taking ranges, the angles must be measured both by the
right and left mekometers with great accuracy. If an error of one
minute is made in any angle due either to the mekometer being out
of adjustment, or to a bad coincidence being made, there will be an
error in the range found of 100 yards at 3,000 yards (if a base of 25
yards is used). One minute is the angle subtended by one inch (or
a halfpenny) 100 yards distant.
The adjustment of the instruments being correct is of much
greater importance than the length of the cord being correct. If a
25 yards cord is 9 inches short the range found will be 1 per cent,
too long, i.e., 80 yards at 3,000 yards.
If both right and left instruments are in perfect adjustment and
the right is set at infinity (/ft), each instrument should reflect an
exact right angle L and R (Fig. 18).
Fig. 18.
It is practically impossible to obtain an exact right angle in the
field upon which to test a mekometer, but provided that the two
angles Lmid R are together equal to two right angles (Fig. 19) the
error in finding ranges will be very small if neither angle varies
more than about 2° from a right angle.
Fig. 19.
The theory of this is considered further on, see page 36.
31
To test the instruments for adjustment is to see that the angles
reflected by them are together equal to two right angles:—
Fig. 20.
О
If three rickets or tripods he placed at points P M T, so as to bo
in a straight ino, and an object nt О bo selected so that the angles
О M T, О M P, are each within 2Q of a right angle, and if the left
and right mekometer (set at infinity) bo placed on M, the object at
О should coincide respectively with T and P (Fig. 20).
Mekometers, when issued for service, are interchangeable and
each is in perfect adjustment, but the same right and left instruments
should always bo used together. They should be occasionally
tested (ясе page 8, Handbook of the Mekometer, Equipment
Regulations, Part I; and Magazine Regulations), and adjusted if
necessary, as described below.
IL—To Ascertain if toe Left Mekometer Reflects л Right
Angle, or Within 2° of a Right Angle.
Place the left mekometer on the tripod at M (Fig. 20) as
before, direct its telescope on 0, and check tho coincidence of 0
and T. Turn tho mekometer until its telescope is directed towards
P. If a perfect right angle is being reflected, 0 should now be
seen in coincidence with P.
If M P is 100 yards and the reflected image of 0 appears more
than 20 feet right or left of P, the mekometer is more than 2
degrees out, and tho adjustment detailed in Part III should not be
carried out unless the mekometer is very urgently required for use
and approximate ranges are all that are necessary.
III.—To Test and Adjust Two Mekometers Together. To
Ascertain if the Two Instruments Together Reflect
Two Right Angles. And to Adjust.
Set up a tripod (a “Stand, lamp or heliograph” is most
suitable) at the point M (Fig. 20) and place the hole (for handle)
in the base of the left mekometer over the small projection on the
cap to which the brass chain is attached* Select some well defined
vertical object 0 about 1,000 yards distant. Look through the
mekometer telescope at 0 (an X 6 telescope should always be used
for this purpose ; those issued with tho Artillery mekometers can
18114	C
82
also be used in the Infantry mekometers), and arrange for a
signalling telescope on its stand to be moved to T, so that the
centre of the object glass, when laid on the mekometer vane, exactly
coincides with О. T should be at least 100 yards from M. A
vertical strip of paper may be attached to the centre of tho object
glass (Fig. 21) to lay on :—
Fig. 21.
Remove the left mekometer and, with the signalling telescope
at T accurately laid on the projection on the top of the stand at M,
direct the placing of another stand at P, in line with M, and at
least 100 yards from M; or should there be a wall or building at
the desired position a vertical chalk mark upon this will be more
accurate and convenient.
The points T and P must be laid out afresh for each pair of
instruments to be tested.
Place the left mekometer again on the stand at M, direct its
telescope on 0, and check the coincidence ot 0 and T. Remove
the left mekometer from the stand.
Set the drum of the right mekometer at infinity ), and place
the hole in the base of the mekometer over the projection on tho
cap ot the stand at M. Direct the telescope on 0, and if the mark
at P is found to be in coincidence with 0, the instruments are in
adjustment with one another. If not, proceed as follows :—
(1)	Remove from the cover the small screw which keeps it in
position, and slide the cover forward off the instrument.
(2)	Loosen the keep nut, insert an adjusting pin in the head
of the adjusting screw (F, plan of reading instrument, Plate II) in
the horizon mirror frame nearest to the range drum, and turn the
adjusting screw in or out until 0 and P exactly coincide.
A suitable adjusting pin can be made out of a nail by filing it
to fit. Great care must be taken not to work the adjusting screw
more than is absolutely necessary, as a tight fit is essential, also
not to strain the German silver mirror spring. The last movement
of the screw must move the reflection to the right. Tighten the
keep-nut, and check the coincidence again.
(8) Replace the cover and cheek again to see that the left
mekometer reflects 0 and T in exact coincidence, and the right
mekometer 0 and P in exact coincidence.
(4) If there arc any accurately known ranges, test the meko-
meters on these for correct readings.
Note.—A very small error inlaying out the straight line T M P
or in making the coincidence T 6 and О P will introduce largo
errors into the adjustment.
88
Mekometers adjusted as above will give very good results, and
should never be more than 1 per eent. out at 1,500 yards for
Infantry pattern, or at 8,000 yards with Artillery or G.S. Any
slight errors found are probably due to one of the following
causes:—
i.	The vane, holo in the body and intersection of the direct
and reflected lines of sight not being absolutely in tho
same vortical lino.
ii.	The infinity point not being absolutely in the correct place
with reference to other ranges, due to wear of drum screw.
If when testing as above, it is found that the mekometers are
much out of adjustment, it is probable that some of the internal
mechanism has become deranged, and it is more satisfactory not to
proceed with the adjustment until it has been put right, which
should, as a general rule, bo done by the A.O.D.
When necessary, an approximate right angle may be laid out
as follows:—
Eig. 22.
О
/3?
\ i
\ i
\	i
'	/
t	/
Lay out three pickets P M T in a straight line, as above
(Fig. 22), and at least 100 yards distant from each other to
eliminate errors due to parallax, place the left mekometer at M
and look at P and direct an assistant to place a picket at a distance
of about 100 yards at Oi, so that its reflection is seen in coin-
cidence with P. Turn the left mekometer towards О until the
reflected image of T can be seen, and direct the assistant to place a
second picket at Оз, so that T and O3 are seen in coincidence.
Measure the distance Oi Оз and place a third picket О exactly
half way between them. The angles P M О and T M О will then
be approximately equal, and will be well within 1° of a right angle.
To adjust the left mekometer to read an approximate right angle.
Place tho mekometer at M looking towards O, and turn the
adjusting screw in the Horizon mirror frame until О and T are seen
in coincidence.
IV. Detailed Instructions for Adjustments, which would, as a
RULE, BE CARRIED OUT BY A.O.D.
The following arc some of tho parts most likely to become
deranged:—
1.	Mirror springs losing their strength.—This can be tested by
placing the nail of the thumb behind the mirror and forcing the
mirror very slightly away from the points of the adjusting screws.
If the mirror returns with a click and the instrument reflects tho
same angle as before, the springs are correct.
34
2.	Screws, especially those of the mirror frames, becoming loose.
—The adjusting screws can be tested by inserting an adjusting pin
and observing if the screws turn loosely or not. The screws in the
body can be similarly tested with a screwdriver. Screws whose
heads are painted over need not be tested.
A specially shaped screwdriver (Fig. 23) which can be made
from an ordinary screwdriver' by filing, is necessary for tightening
the nuts above the flanges of the mirror frames.
Fig. 23.
3.	Index arm 1) fright instruments only J altering its position.—
This is not easy to find out. The point of the drum screw should
be more or less opposite the centre of the hardened steel piece in
the index arm. The index arm is kept in position by a plate being
screwed over its spring L to the body of the instrument. If the
instrument is allowed to fall the heavy arm may overcome the
friction between the plate and the spring, and the instrument will
be very badly out of adjustment. Mekometers are, however, tested
before issue by being knocked against a felt covered board to see
that the index arm will not shift. If there is a suspicion that the
index arm is loose, knock the base of the instrument against the
palm of the left hand and note what angle the instrument reflects;
then knock the top of the instrument in a similar manner. If the
same angle is reflected, the arm is not loose.
4.	Mirrors becoming chipped near the points of the adjusting
screws.—The only remedy for this is to fit new mirrors, which
should not be done unless really necessary, and never in the case
of the index mirror in the right instrument, except in case of
emergency.
To FIT A HORIZON MIRROR IN EITHER INSTRUMENT, OR AN INDEX
MIRROR IN A LEFT INSTRUMENT.
(a) Take the mirror frame out of the body, by removing the
nuts and screws.
(ft) Remove mirror retaining springs and damaged mirror.
(c)	Scrape 8 small pieces of the silvering from the back of the
new mirror, so that the points of the adjusting screws can touch the
glass.
(d)	Insert new mirror, seeing that it is not too tight or too
loose a fit, and that the top holding screw is just clear of it.
(e)	Replace retaining springs, care being taken to see that the
springs have sufficient strength and their points are exactly opposite
the points of the adjusting screws. The mirror should be moved
slightly forward to see that it does not hang up in its frame.
(У) Refix the mirror frames in the body, being careful that all
screws are well tightened up. Paint over heads of screws.
(</) Get the vertical adjustment of the mirrors correct (i.e.—
when looking in the mekometer two vertical lines, one seen by
direct and the other by reflected vision, should coincide or be
parallel to one another, and not cross one another at any point).
This is effected by turning the top adjusting screws in the mirror
frames. Care must be taken not to strain the retaining springs.
35
To FIT AN INDEX MIRROR IN THE BIGHT INSTRUMENT.
(a)	Remove the horizon mirror frame.
(b)	Remove the complete index mirror arm, by taking out tho
three screws on the right side of the body.
(c)	Fit a new mirror as described above.
(d)	Replace index mirror frame, being specially careful that
the screws are very firmly fixed and that the hardened steel piece
in the arm is opposite the point of tho steel screw when the range
drum is at zero.
(e)	Replace horizon mirror frame, and note that the index arm
does not foul it.
(/) See that index arm follows the movement of the drum
throughout its run.
(7)	Correct vertical adjustment.
V.—Checking and Adjusting on a Known Range.
If the range to a distant object is really accurately known,
which is seldom the case, it is quicker and того accurate to adjust
the mekometers to road correctly to that range. The range of tho
object should bo at least as long as any that tho mekometer is likely
to have to find.
Erect a tripod at L (Fig. 21) and place tho loft instrument on
Fig. 21.
О
it with its telescope directed at 0. Erect another tripod, with tho
right mekometer upon it, at R, in such a position that tho vane of
the mekometer appears to be coincident with 0 when seen through
the left mekometer; and that the distance L R is exactly 25 yards
(or 50 yards for Artillery mekometers). Sot tho drum of tho right
mekometer at tho range of the object and look through the
telescope. The vane of the left mekometer should thou coincide
with 0. If it does not, adjust by turning tho adjusting screw as
laid down in III.
If the ranges of other objects aro known, check tho mekometer
on them.
36
VI.—Theoretical Consideration of the Error Introduced in
Finding a Range, when the Left Mekometer does not
Beflect a Perfect Right Angle, but the Two Instru-
ments (with the Right Set at Infinity) together
Reflect Two Right Angles.
Fig. 25.
T
L R
In Fig. 25 let T be the target, L and R the position of the left
and right mekometers. The range T R or T L is then equal to L R
cot L T R.
Suppose, however, that the left instrument reflects T Li R, or
T L2 R, instead of a right angle, Fig. 26, the left instrument will
have to be placed at Li or L2 instead of L (the distance between
the two instruments being always the same), and R will be nearer
to the line T Lj L2 than it was in Fig. 25. The range will still
equal L R cot LT B, but now L R is shorter than it was in Fig. 25.
Fig. 26.
Ti
The instrument which is graduated for a base Li R, or L2 R, is
being used with an effective base L R. In other words, the ranges given
in Figs. 25 & 26 are inversely proportional to the lengths of L R in
these two figures. If the angles reflected by the left mekometer do
not vary from a right angle by more than 2°, the range found will
not be more than wrong. This amount will always be plus.
FORM I.
Form of recording Ranges taken at Drill or Inspection.
Place_______________________________
Date __________________________,
Name of i State of the observer, j weather.	Number and mark of I instrument.	Object observed.	Observed range.	1 True range, I stating how 1 determined.* )	i Length of  base. i i	Time.	Remarks.
i -- 	 - — -			i I	5	i I	• 1 i			
Signature of Officer.
* In verifying by Ordnance Map, the scale on the map itself must be used, not a graduated ruler, because the paper is liable to stretch and shrink.
88
The following syllabus will be adhered to in the examination
of officers in (a) Regimental Duties, drill and field training,
Artillery (VII) Range-taking, King’s Regulations, Appendix XI, and
in the test of range-takers for proficiency pay.
Note.—The tests for Infantry Range-takers will be found in
Musketry Regns., Part I.
EXAMINATION IN FIELD RANGE-TAKING
FOR ARTILLERY.
Mekometer.
The examination is divided into four sections, viz.:—
(i)	Verbal examination in the following:—
(a)	Errors of manipulation and their results^
(5)	Rules for Range-takers ...........
(c)	Care and preservation of the instru-
ments ...	....................
(d)	Tests to ascertain if the instruments are
in adjustment .........................
(ii)	Examination in “reading instrument ”	... 100	„
(iii)	Examination in “right-angling” ......100 „
(iv)	For drill and style ......................25	„
800
To obtain a pass, 75 per cent, of the total marks must be
obtained.
For sections (ii) and (iii) in the above examination, four
service objects are selected at the following distances; two under
8,500 yards, one about 4,000 to 4,500 yards, and one over 5,000
yards. The time allowed for the two former is 1 min. 80 secs.-
each, for the two latter 2 min. each. In (ii) an instructor acts as
right-angle man; in (iii) the instructor having the reading
instrument set at the ascertained range, observes the correctness or
otherwise of the right-angling. In each of these sections 25 marks
are allowed for each range.
The scale of deductions for inaccuracy or over time in the above
examinations is as follows:—
For inaccuracy—
Up to 1J per cent, of range ...
As reading From 1| to 2J per cent, of range .
man.
From 2| to 4 per cent, of range
Over 4 per cent, of range ..............
For each 0. R.* or C. L.* ..............
For each W. i...........................
If three W’s+ are recorded at any
range, all the marks for that range
are forfeited.
Deduct.
Nil.
5
10
All marks.
2
5
As right-
angle man,
stationary,
or moving
objects.
For over time—
* Not exceeding 5 secs, over time
M	M	10	,,	,,	,J
„	»	15	„	„	„
Exceeding 15 secs.........
2
5
15
All marks.
* An observation on the correct object, but on the right or left edge of it.
f An observation wide of the correct object.
89
INDEX.
PA (IE.
Adjustment of left instrument to reflect an approximate right angle ..	33
„	of right and left instruments together ..	..	..	..	31
„	on a known range	..	..	..	..	..	..	..	35
„	vertical ..	..	..	..	..	..	..	..	31
Artillery mekometers	..	..	.,	.,	..	..	.,	..	1
Base, double, use of ......................................... 8, 9, 25
„ extending the	..	..	..	..	..	..	..	. .	9
„ half, use of........................................................8,	25
Cleaning mirrors ........................................................ 28
„ telescopes ,.	..	.,	..	. .	..	,.	..	23
Coincidence, making ..	..	..	..	».	..	..	. . 10» 12
Cord ..................................................................... 0
„ repair of . .	.	,	..	..	..	..	..	. .	..	23
Drum graduations	..	..	..	..	..	..	..	..	4
„ reading ..	,	.	..	...	..	..	. .	. ,	. .	10
Errors due to left instrument not reflecting a right angle .,	..	..	36
„	of observation	,	. .	..	..	..	..	..	20,	21, 22
„	of base cord	.,	..	..	..	..	..	..	..	22
Extending base ..	..	..	..	..	..	..	..	9
Field sketching ..	..	................................ ..	20
G.S. mekometer	.,	.,	. .	..	..	..	..	. .	..	2
General instructions for range-taking..................................... 7
Handles ..	..	..	..	..	.	..	..	..	..	5
Holding the mekometer ..	. .	..	. .	..	. .	9
Inaccessible points, to find the distance between , ,	..	..	..	27
Inaccurate instruments ..	..	..	.,	..	..	..	. .	14
Index mirror, to fit now	..	..	..	..	..	..	.. 34, 3.5
Inspection, weekly ..	..	..	..	..	..	..	..	23
Instruction in drill halls ............................................   18
Leather cases ............................................................ 6
Mirrors, chipped ..	..	..	..	.,	..	.	..	..	34
„ cleaning........................................................... 23
„ replacing .......................................................34,85
Moving targets ..	.,	..	..	..	..	. .	..	..	12
Observing, best objects for	..	..	..	..	..	..	.	13
Preparation of instruments	..	..	..	.,	..	..	..	9
Qualified officers ..	..	..	..	..	..	..	..	..	29
Range-taking, general instructions........................................ 7
Range, taking the, with reading instrument only........................24,	25
„ taking tho ........................................................ 18
Range-finding triangle ..	..	..	. .	..	..	..	10
Reading instrument, carrying...............................................0,	7
„	„ description ..	..	..	..	..	..	3
Reels, carrying........................................................... 7
„ description ......................................................... 5
Repairs, cord ..	.......................... ..................... 23
„ horizon mirrors ..	..	..	..	................ 84
„ index mirrors ..	................... .....................34.85
Riglit angle instrument, carrying .........................................0,	7
„	„	„ description............................................ 2
Right angle, obtaining the ..	..	..	..	..	..	..	10,17
„	„ to lay out in tho field	..	..	..	..	• *	..	83
Springs, mirror, testing ..	..	..	..	..	..	..	..	34
Syllabus for examinations in	field range-finding ........................ 88
Telescopes................................................................ 4
Testing ..	..	.................... • •	..	. •	..	8
„	artillery mekometers	.,	..	..	♦ ♦	..	..	..	28, 30
„	G.S. mekometers	............................................ 29
„	Infantry mekometers	..	..	..	. •	•.	..	..	28
Theory of instruments .,	. •	.......................... l’V/’f 8C(1*
Vane ..................................................................... 4
18114	1)