A. By using the range-arm that is constructed for the scale to which the board is drawn, setting the zero on one point and reading the number of yards on the arm where the point cuts the scale-edge.
Q. How is the longitudinal deviation measured on the plotting-board?
A. Measure the distance from the gun to the target, and from the gun to the splash. Subtract the lesser from the greater, and this will be the longitudinal deviation, according to the meaning given in drill regulations.
Q. How is the lateral deviation measured?
A. Read the azimuth of the target and splash from the directing-gun. Subtract the lesser from the greater: result = lateral deviation. If the azimuth to the target be greater than that to the splash, it is seen that the deviation will be to the left and vice versa.
Q. How are open sights on rapid-fire guns used?
A. The same as on small-arm pieces; i.e., the range in yards or elevation in degrees and minutes is set on the rear sight according to how the sight is graduated, and the gun is elevated and traversed until the target, front sight, and rear sight all come in line.
Q. Describe the 5" R.F. sight.
A. It consists of a sight-bar graduated in degrees and minutes (lowest reading being six minutes), with a sliding scale at the top for deflection right or left, the deflection-scale reading to three minutes. A range-drum is also geared to the sight-bar, and moves with it in such a manner that when the piece has a certain elevation it will shoot to a distance equal to the range on the drum. This avoids using any range-table.