FDC General Knowledge For Fire Control Specialist (13J) Practice Test

The main idea is that azimuth and deflection describe horizontal angles in aiming, but from different reference frames. Azimuth is the horizontal angle from a fixed reference direction (like true or magnetic north) to the line to the observed point, using the reference direction as the vertex. Deflection is the horizontal clockwise angle from the line of fire to the line to a designated aiming point, with the vertex at the sight, representing the adjustment you must make to bring the gun onto target. This distinction makes the described statement the best: it correctly defines azimuth as the reference-to-target horizontal angle, and deflection as the gun-line-to-designated-point horizontal angle with the vertex at the sight. The other options misstate the nature of these angles: azimuth is not a vertical angle, nor is it a distance, and they are not the same angle.