THE ROYAL ARTILLERY INSTITUTION. 
193 
Lay tlie short telescope on the white face of the opposite angle-finder, 
we thus get an index number (m); set the breech of the gun, on line C, to 
this number on D. 
Lay the short telescope onthe muzzle of the opposite gun, note the 
index number n on line A or B of the roller; take n over this on B or A, 
we thus get a number p. Now set the mark (made) on H to the large 
figures, giving^ on line G. Then the tape mark will point to the true 
distance between the guns. 
Measure the distance with the tape, and if it does not agree with the 
true distance, shorten or lengthen the tape until it does. 
Note. —It is evident^? = m ~ n, or else p = m + 100 — n. 
Note. — If the guns are placed nearer the 40 yds., the mark on H 
may haye to be set to the smaller figures on G, and not to the large ones. 
To obtain the Range without using the Tape. 
Be particular in bringing up the guns to see that they are more than 
usually square, proceed as usual at the pivot gun, only do not run out 
the tape, also do not call out the index number until the roller gunner 
shows by a sign* that he requires it. 
At the outer gun, take the index number as usual, and record it as 
usual on the roller, by bringing the breech mark on C, under the index 
number on D. 
Then direct the wires of the short telescope until these are on the 
muzzle of the opposite gun, make this the “ muzzle-number ” now shown 
by the index. 
Seek the muzzle number on lines A or B (no matter which), opposite 
to it, on B or A will be “ the muzzle difference number.” Set the gun 
mark on H to the muzzle difference number on G. 
Now get the index number from the pivot number, and proceed as 
usual, that is :— 
Note on C (the red figures) this number over it, on D is another 
number, follow this up to E, and above this figure on E is the range. 
This is strictly true, if the guns are less than 110, or more than 34 
yds. apart; if they are nearer than 34 yds., and if the muzzle difference 
number is, say, 60, the gun mark on the line H may not have to be set 
to 60 on the line G, but to the division marked 6. 
The fact is that there are several 60’s on the flat face of the roller, 
but only that usually employed is marked 60, the others are marked 6. 
As long as the guns are over 40 yards apart, there can be no doubt; 
in this case the gunner sets the gun mark on line H to the numbers 
running from 40 to 30, which are marked in full. If the distance 
between the guns is less than 40 yds., the gunner can tell which is the 
right number, say 50 or 5, by observing how far the guns are apart, and 
remembering that if the muzzle difference is properly set, the tape mark 
must also point to the actual distance between the guns. 
Figuring of the Roller. 
Lines A, B, C, and D, are each simply divided into 100 equal parts. 
Line E, commencing at 0, is marked 10, 20, 30, 40, 50, 60, 70, 80; 
beyond 80 will be seen 1, 2, 3, 4, 5, 6, 7, 8, 9, which mean 81, 82, &c., 
89; we then come to the 0 at which we set out, and this may mean 90; 
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