98 ADJUSTABLE POINTERS. 
mands. There are two or three ways of altering existing pointers to 
effect this, but I will deal with the simplest first. 
We will suppose the ordinary group of 410” R.M.L. guns, 15 feet 
apart (the distance varies but this is about the least asa rule). The 
length of a degree (with 21:7 feet radius of arc) is about 4 inches and 
the ¢ degree marks are 1 inch apart. 
Now with No. 2 gun as the gun of direction, corrections must be 
given to the angles of training of Nos. 1, 3 and 4 as follows :— 
At 1200 yards, 15 minutes is equivalent to 15 feet, thus at 1200 
yards a correction (with the guns in the centre) of + degree to 1 and 
3 and 4 degree to 4 will concentrate the fire of the group at that 
range, similarly— 
At 2400 correction for 15 feet = 74 minutes or 4 inch. 
»» 3000 ” 9 » = 69 ” RR DD 
-», 3600 ” ” » = 96 ” » B 9» 
», 4200 ” ” » = 46 re) mee x 
», 4800 ” ” » = 3% 2 9 2% 
As + degree on the arc = 1 inch. 
Oo Oe TOUTS, pg SN gy 
it will be thus sufficient (at that training) to move the pointer of 1 and 
3 4 inch and that of 44 inch inward in order to concentrate at even 
4800 yards. 
The concentration for the intermediate ranges will vary in proportion 
but as the divisions would be too small on that scale a multiplying 
arrangement becomes necessary. On examining the present service 
pointer it will be seen that it can be turned round on its longer axis 
through a semicircle. 
It is necessary only to fix a small brass pointer to its edge as shown 
in Fig. 1. The revolution through a } circle will move this pointer 1 
Fie. 1. 
inch to one side. A revolution through a $ circle about 4 an inch and 
so on. 
