COMPLEMENT VALUE. ANOTHER COUNTER CIRCUIT COUNTS UNSECCESSFUL TRANSMISSION AND RECEPTION (RANGING) PERIODS AND AFTER A REDETERMINED NUMBER OF CONSECUTIVE SUCH PERIODS THE SYSTEM SWITCHED FROM THE TRACK OF THE ACQUISITION MODE.

A DIGITAL SYSTEM FOR MEASURING THE RANGE OF A REMOTE OBJECT IN RESPONSE TO LASER ENERGY REFLECTED FROM THE OBJECT AND FOR CONTROLLING THE MODE OF OPERATION. WHEN LOGIC CIRCUITS DETERMINE THAT A SIGNAL IS A VALID RETURN SIGNAL (I.E. NOT NOISE ENERGY) THE SYSTEM SWITCHES TO A TRACK MODE OF OPERATION WHEREIN IT RESPONDS ONLY TO SIGNALS CONCIDENT WITH A RELATIVELY NARROW TRACKING GATE. IF THE RETURN SIGNAL SHOULD FADE (DETECHABLE SIGNAL NOT RECEIVED) A COUNTER, WHICH STORES THE DIGITAL COMPLEMENT OF THE RANGE INFORMATION AND WHICH POSITIONS THE TRACKING GATE, IS AUTOMATICALLY RECYCLED TO THE LAST STORED RANGE