OPERATION.
The bar is clamped by means of the screw near the left end of the ruler.
The bar must be held firmly while moving the trammel. In making corrections for artillery fire the following data, as obtained at the opening of the action, will usually suffice for the entire action.
Density of the air,
Velocity of the wind,
Azimuth of the wind,
Height of tide.
The range effects and deviating effects of the wind must be obtained for each shot. Tide should be changed at least every half-hour. As soon as the density of the air is ascertained the computer will insert a pin, or set the pointer at the top of the corresponding curve. The same will be done for height of tide.
The muzzle velocity to be used for the first shot will be marked in a similar manner as directed by the range officer. The wind-component device having been set for the azimuth and velocity of the wind and the azimuth of the target, the computer will note the reference-number and set the pointer at the top of the wind-curve having that number.
THE RANGE-BOARD.