48 
MINUTES OE PROCEEDINGS OE 
Now, CX and BZ are the distances from the face of one angle-finder to 
the pivot of the other, and this may be taken in practice as equal to the 
base, or 40 yds., or 1440 ins. CZ and BX are the distance from the faces of 
the angle-finders to their own pivots, equal to 3 ins. 
Hence, 
and therefore, as small angles vary as their sines. 
Similarly, 
9 480 \2 J 
Y 480 \2 / 
, 1 
or we shall have an error of about two per thousand in our apex, and con¬ 
sequently in our range. This, again, is too little to affect our elevation. 
Let us now assume a case, and see what will be the difference between 
the sides of the triangle, as obtained by the calculating roller, and as 
obtained by the ordinary method. 
A 
Let BC = 40 yds. 
ABC = 35,82 a= 89° 83' 
ACB = 35,46 = 88° 89' 
71,28 178° 12' 
.-. BAC = 72= 1° 48' 
and will be read by the angle^finders 
