Digital bearing readout for sector scan sonar

Claim 1

IN A SECTOR SCAN PULSE SONAR SYSTEM IN WHICH ENERGY PULSES ARE PERIODICALLY TRANSMITTED AND ECHOES OF THE TRANSMITTED PULSES RETURNED BY A DISTANT TARGET ARE UTILIZED TO BRIGHTEN A SPOT ON THE VIEWING SCREEN OF A CATHODE RAY TUBE IN AN AZIMUTHAL POSITION CORRESPONDING TO THE BEARING OF THE TARGET AND ALONG A SCAN LINE HAVING LEADING AND TRAILING EDGES CONTROLLED IN TIME BY A SCAN GENERATOR AND OF KNOWN BEARINGS, BEARING READOUT APPARATUS INCLUDING: A COUNTER, MEANS OPERATIVE UNDER THE CONTROL OF THE SCAN GENERATOR TO READ INTO THE COUNTER THE BEARING OF ONE OF THE EDGES OF SAID SCAN LINE, A FIXED FREQUENCY OSCILLATOR, A HAND MANIPULATED LIGHT SENSITIVE PROBE OPERATIVE WHEN PLACED OVER A BRIGHTENED SPOT ON SAID SCREEN TO PROVIDE A CONTROL PULSE, AND MEANS UNDER THE JOINT CONTROL OF SAID SCAN GENERATOR AND SAID CONTROL PULSE FOR CONNECTING SAID COUNTER TO SAID OSCILLATOR DURING THE TIME INTERVAL BETWEEN THE OCCURRENCE IN TIME OF SAID ONE OF SAID SCAN LINE EDGES AND OF SAID CONTROL PULSE.