adapt the geometric conditions to the arrangement of the movable parts and to consider eventually a certain function of the lead angle for example the transformation of sin u03c6 into u03c6 pursuant to the invention the following mathematical equations may be programmed into the computer 3 for the execution of the calculations it is felt to be within the abilities of those of ordinary skill in the art of programming digital computers to be able to construct a program which will solve the trigonometric equations set forth herein the angle u03b3 in the setting plane fig1 between the two sighting beams may be determined from the specific values of the two sighting beams s 1 and s 2 and may be expressed as follows cos u03b3 sin u03bb sub 1 sin u03bb sub 2 cos u03bb sub 1 cos u03bb sub 2 cos u03b4 u03b1 1 the equation equ1 may be used to determine the angle of the apparent direction of the setting plane and respectively the apparent flight direction if the airborne target moves on a horizontal straight path 34 a 34 the lead angle u03c6 is determined by the equipment location g the target position z and the lead point v that is the lead angle u03c6 is located opposite the lead distance zv which may be conceived as the radius of a horizontal circle exhibiting the lead point v as the center and representing the geometrical site of all possible target positions to the.