THE ROYAL ARTILLERY INSTITUTION. 
191 
In deploying, or forming line for action from other columns, the gun 
that comes up first into action becomes the pivot. 
Use of the Roller in taking the Range. 
The ordinary straightforward method of taking the range is when the 
range is considerable, and more than 25 times the distance between the 
guns, and when a tape is used. 
Instructions for Calculating Range with Roller. 
(1) Set the tape arrow, on line E, to whatever number on line E the tape 
measures. 
(2) Set the mark, on line C (in the shape of the breech of a gun), to the 
index number called out at either gun. • 
(3) Note on the large red figures , on line C, the index number given at the 
other gun, over this is a number on line D; above the corresponding number, 
on line E, will be found on line E the range. 
It is extremely improbable that in a campaign a gunner will require 
any knowledge of the roller beyond the above: there are, however, some 
secondary uses of the roller. 
Secondary Uses of the Roller. 
To determine a range when the range may possibly be less than 25 
times as great as the distance between the guns. 
Suppose the guns are 90 yds. apart, it will be easily comprehended 
that the word tape must be brought under 900, as there is no 90 on the 
roller. 
Let us, in addition, suppose that our gun numbers are 30 and 20. 
According to our rule, if we set the breech of the gun at 30, over 20, 
on line C, we find 50 on it, and over 50 on E, we find a range of 
4,120 yds., which may be quite right. 
But suppose that the range does not appear to be nearly 4,120, can 
we have another range corresponding to 50 P 
Yes. 
Below the 0, on E, we see the figures 9, 8, &c.; these really mean 
90, 80, &c.; and we shall find over the 5 or 50, 1,378, which may be the 
true range. 
Can there be another true range ? 
Yes. 
Counting back 10 divisions from 5, we come to a number marked 75, 
but which might also be considered 50; over this is a range of 824 
yards. 
There are, then, three possible true ranges, 4,120, 1,378, 824, and, 
indeed, there are several other true ranges, all smaller than 824. 
The question will arise, “ Does not this lead to uncertainty in the 
ranges ?” 
Practically, ~No : because the finders will be chiefly used between 
1,000 and 4,000 yards; and if a distance of about 40 yards be kept 
between the guns, there can, within these limits, be no ambiguity. 
Occasionally, to insure greater accuracy, large bases of 90 yards may 
be employed ; the gunner is then liable to the above ambiguity, but the 
