The vertical angle unit shall be capable of receiving and recording a mechanical input of observer vertical angle, designated in mils measured as positive above the horizon and negative below the horizon, and converting this input to an electrical output value. This output value is equivalent to the tangent of observer vertical angle, which is proportional to the product of observer distance and observer vertical angle. The vertical angle unit is a functional plug-in subassembly of the Gun Direction Computers: Ml5 and M15C.