Angle of Departure.—The angle made by the line of departure with the horizontal. (d in [Fig. 102].)
Angle of Elevation.—The angle made by the axis of the piece with the horizontal. (q in [Fig. 102].)
The Jump.—The difference between the angle of elevation and the angle of departure, owing to the movement of the gun at discharge. (j in [Fig. 102].) (The jump of 3.2 in. and 3.6 in. guns varies from 20 minutes at 1 degree to 30 minutes at 10 degrees elevation.)
Initial Velocity.—The velocity of the projectile at the muzzle.
Remaining Velocity.—The velocity at any point of the trajectory.
Final Velocity.—The velocity at the end of the range.
Range.—The horizontal distance from the muzzle to the point where the projectile strikes.
Drift.—The departure of the projectile from the plane of fire. With guns having a right-handed twist it is to the right, and its extent varies nearly as the square of the range.
Direct Fire is from guns with service charges at all angles of elevation not exceeding 15°.