Abstract: Each bin of a one-thousand stage shift register represents a two-tenth mile aircraft to ground station interval, and the register is shifted a full cycle corresponding to a two-hundred mile spacing. During a first shifting epic, all pulses returned from the ground station are inserted into the bins in timed relationship to each other and to transmitted pulses. In subsequent epics, stored pulses from the register are reinstated therein if there is time coincidence with another received signal. Once the register contains one-and-only-one signal, corresponding to the aircraft to station distance, that signal is automatically reinserted for the next three epics, regardless of signal receipt. Further coincidence of a receive signal, however, resets the automatic regeneration for three more periods, and so on. After three periods without a coincidence, all signals are passed to the register during the next epic.