ADJUSTABLE POINTERS. 101 
top of the bolt so that the index can be set to either of the scales one 
of which is for the centre of the arc and the other for the extreme right 
and left. 
Or else the index might be made to set back at the collar a certain 
amount to allow for extreme trainings. With the swinging pointer 
index and a horizontal drum this training correction can be carried to 
high degree of accuracy and might be especially useful when firing 
group salvoes at long ranges from high angle guns worked by position- 
finder. 
When laying the process is simple enough. The gun-layer pushes 
his index up or down according as it is extreme training or not, and 
when the final range is called out he sets it at that range and then 
traverses his gun to the training called out. With the swinging 
pointer a clamp should be provided and with the revolving pointer a 
little rack with notches just under the handle H will hold the bolt 
steady. The power of thus concentrating at will should prove a great 
advantage, making practice more attractive and easier for the operators 
to correct and estimate their shots. 
On the greatly increased fire effect it is perhaps needless to dwell as 
it is surely obvious. 
APPENDIX A. 
Fie. 5, 
Go ® where eC es 
. z = 100 yards. 
8 Se oN gee interval 
at aha: ES FS sects euns. 
Substituting values of r and +’ we have at 1200 yards 
range— 
—_ 9 x 100 _ Syards 
1200 12 
= 15 inches. 
T 
.*. lateral error at 1100 yards or 1800 yards = 15 ins. 
For 4800 yards we have—. 
2 ® 6 100 eS yacels aE te 
4800" 7 28 Panga ; 
ee ce el ee eo ee 
5 YoDs 
therefore to concentrate within 15 inches or 2 feet according to 
interval of guns it will be sufficient to divide the scale at every 
100 yards up to 2400 yards andbeyond that at every 800 yards up to 
4800 yards. 
