THE ROYAL ARTILLERY INSTITUTION. 
49 
Prom tlie method employed by the finders we shall have 
40 
AC = AB = 
sin 71*85 
40 
71*85 
20 
800 
71*85 
= 1275*9. 
By the ordinary method we have 
sin C 
sin 20 
114*593 
AB = BC 
— 40 
AC— BC 
sin^ 
sin 35,46 
sin 72 
sin B 
1273*1 ; 
sin A 
_ 4Q sin 35,82 _ 1373 . 4 _ 
sin 72 
Here we see our error is less than 3 yds., but we cannot change our 
elevation less than one minute, which, at 1275 yds., gives 6 J yds.; hence 
our range is practically exact. 
It may often happen in the field that, owing to bad ground, the guns 
cannot be drawn up so that the object is directly in front of the interval; 
but as long as the object is not much to the flank, the ranges obtained by 
the angle-finder will be sufficiently accurate for all practical purposes. 
If the dressing of the guns is much oblique, it will be at once detected 
by the steel limb of one finder running off the index. 
*■ 
7 
