Calibrating heading systems

Claim 1

A METHOD OF CALIBRATING AN AIRCRAFT HEADING SYSTEM TO A CELESTIAL REFERENCE, WHICH COMPRISES GENERATING A HEADING OUTPUT ANALOGUE SIGNAL CORRESPONDING TO AN ASSUMED HEADING; GENERATING AN ANALOGUE OF CALCULATED AZIMUTH OF A SELECTED CELESTIAL REFERENCE BODY; SUBTRACTING ALGEBRAICALLY THE FIRST MENTIONED ANALOGUE AND THE SECOND MENTIONED ANALOGUE WHEREBY TO PRODUCE AS A FURTHER ANALOGUE SIGNAL THE ANALOGUE SIGNAL OF AN ASSUMED RELATIVE BEARING OF SAID CELESTIAL BODY TO SAID AIRCRAFT; DRIVING A HEADING RING IN A SEXTANT MOUNT, WHICH RING BEARS A ZERO INDEX MARK AND IS MOUNTED TO MOVE INDEPENDENTLY OF THE SEXTANT, IN RESPONSE TO SAID FURTHER ANALOGUE SIGNAL TO A POSITION OF SAID ZERO INDEX MARK RELATIVE TO THE AXIS OF THE AIRCRAFT CORRESPONDING TO SAID ASSUMED RELATIVE BEARING; ALIGNING SAID INDEPENDENTLY MOVABLE SEXTANT WITH THE ACTUAL BEARING OF SAID SELECTED CELESTIAL REFERENCE BODY; AND INDEPENDENTLY ALTERING THE CALIBRATION OF THE HEADING SYSTEM TO MOVE THE ZERO INDEX MARK OF SAID INDEXED HEADING RING INTO OPTICAL ALIGNMENT WITH SAID CELESTIAL REFERENCE BODY, WHEREBY SAID FIRST MENTIONED ANALOGUE BECOMES THE ANALOGUE OF THE CORRECTED HEADING OF THE AIRCRAFT, CORRECTED BY REFERENCE TO SAID CELESTIAL REFERENCE BODY, THEREBY CALIBRATING SAID HEADING SYSTEM.

Claim 2

A METHOD OF CALIBRATING AN AIRCRAFT HEADING SYSTEM TO A CELESTIAL REFERENCE, WHICH COMPRISES GENERATING A HEADING OUTPUT ANALOGUE SIGNAL CORRESPONDING TO AN ASSUMED HEADING; GENERATING AN ANALOGUE OF CALCULATED AZIMUTH OF A SELECTED CELESTIAL REFERENCE BODY; SUBTRACTING ALGEBRAICALLY THE FIRST MENTIONED ANALOGUE AND THE SECOND MENTIONED ANALOGUE WHEREBY TO PRODUCE AS A FURTHER ANALOGUE SIGNAL THE ANALOGUE SIGNAL OF AN ASSUMED RELATIVE BEARING OF SAID CELESTIAL BODY TO SAID AIRCRAFT; DRIVING A HEADING RING IN A SEXTANT MOUNT, WHICH RING BEARS A ZERO INDEX MARK AND IS MOUNTED TO MOVE INDEPENDENTLY OF THE SEXTANT, IN RESPONSE TO SAID FURTHER ANALOGUE SIGNAL TO A POSITION OF SAID ZERO INDEX MARK RELATIVE TO THE AXIS OF THE AIRCRAFT CORRESPONDING TO SAID ASSUMED RELATIVE BEARING; ALIGNING SAID INDEPENDENTLY MOVABLE SEXTANT WITH THE ACTUAL BEARING OF SAID SELECTED CELESTIAL REFERENCE BODY; AND INDEPENDENTLY ALTERING THE CALIBRATION OF THE HEADING SYSTEM TO MOVE THE ZERO INDEX MARK OF SAID INDEXED HEADING RING INTO OPTICAL ALIGNMENT WITH SAID CELESTIAL REFERENCE BODY, WHEREBY SAID FIRST MENTIONED ANALOGUE BECOMES THE ANALOGUE OF THE CORRECTED HEADING OF THE AIRCRAFT, CORRECTED BY REFERENCE TO SAID CELESTIAL REFERENCE BODY, THEREBY CALIBRATING SAID HEADING SYSTEM.