The set forward point was the anticipated position of the target at the end of the dead time plus the time of flight (see Figure 1).

Next, a slide rule-like device called a set forward rule was used to mark off the set forward point (the green square in Figure 1) for the target.

The set forward point was expressed in terms of firing data: a range (in yards) and an azimuth (a compass heading in degrees) at which the gun/s should be pointed by the gun crews in order to hit the target.

The dials on the face of the gun arm center were used to calculate the angular travel (in degrees and hundredths) of the target between successive plotted points on the board, a quantity that could be corrected (using output from a deflection board) and then applied to calculating the set forward point.