North reference makes homing easier

The earlier Type 72X demanded substantial mental geometry from a trained observer because signal timing did not translate directly into a compass course. The operator had to treat both the watch dial and the space around the aircraft as circles, calculate the relative angle, and then take the reciprocal bearing toward the ship. An improved Type 72D was already in development when radar's priority at the masthead forced the redesign that became the lower Type 72DM installation. On the Type 72DM, a chronometer-controlled mechanism drove the aerial at exactly one revolution per minute and brought the beam through true north at zero seconds. That stable north reference made a signal at fifteen or thirty seconds much easier to interpret as a cardinal direction home. Gearing and motor controls kept the lower, mast-encircling installation aligned even while the ship changed course. The improvement reduced ambiguity before the Type 72DP shifted still more interpretive work away from the aircraft.