DIFFERENCE CHART
for
10 in. B.L.R. No.1
in Battery __________, Fort __________
Directing Gun of that Battery
10 in. B.L.R. No.2
Azimuth of Gun No.1 from Directing
Gun, 79°03'
Gun Displacement, 38 Yards.
Fig. 77.
Fourth: From this same point on the little lever-arm run a pencil along the nearest line parallel to the arrow, and where it intersects the diameter of the disc perpendicular to the arrow is read the component in the direction of deflection or the lateral component.
Q. What is a difference chart?
A. One that determines the differences in azimuth and range between the directing-gun and the gun for which it is constructed. It consists of a board having drawn on it circles of different diameters, which are the azimuth difference circles (the amounts being written on each circle). (See Fig. 77.)
Q. How is it used?
A. First: Set the range-arm on the given azimuth.