Photosensitive device for determining relative rotation

Claim 1

IN AN INERTIAL INSTRUMENT: A BASE; A SUPPORT MOUNTED ON SAID BASE BY GIMBAL MEANS FOR RELATIVE ROTATION WITH SAID BASE ABOUT A PAIR OF MUTUALLY PERPENDICULAR AXES; A SPHERICALLY SHAPED MEMBER UNIVERSALLY SUPPORTED BY SAID SUPPORT FOR ROTATION ABOUT A SPIN AXIS; MEANS FOR DETECTING RELATIVE MOTION OF DISPLACEMENT OF SAID SUPPORT WITH RESPECT TO SAID MEMBER, SAID DETECTING MEANS COMPRISING A PATTERN OF CONTRASTING AREAS ON SAID MEMBER INCLUDING A REFLECTING SURFACE POSITIONED ADJACENT TO A RELATIVELY NONREFLECTIVE SURFACE AT EACH POLE OF SAID MEMBER, THE LINES SEPARATING SAID TWO CONTRASTING AREAS AT EACH POLE BEING PORTIONS OF A GREAT CIRCLE SUBSTANTIALLY INTERSECTING SAID SPIN AXIS AT EACH POLE OF SAID MEMBER, THE NONREFLECTING SURFACES AT THE POLES LYING ON OPPOSITE SIDES OF SAID GREAT CIRCLE; A ROTOR ILLUMINATING MEANS MOUNTED ON SAID SUPPORT TO ILLUMINATE SAID PATTERN AT EACH POLE OF SAID MEMBER, AND TWO OPTICAL POCKOFF MEANS POSITIONED AT DIAMETRICALLY OPPOSITE LOCATIONS ON SAID SUPPORT, EACH ADAPTED TO OBSERVE A POLE REGION OF SAID MEMBER AND SENSE THE AMOUNT OF REFLECTED LIGHT FROM SAID PATTERNED SURFACE, PROVIDING OUTPUT SIGNALS INDICATIVE OF REFLECTED LIGHT SENSED THEREBY; A SUMMING MEANS CONNECTED TO EACH OF SAID PICKOFF MEANS FOR THE PURPOSE OF PROVIDING AN OUTPUT SIGNAL INDICATIVE OF THE SUM OF THE SIGNALS APPEARING AT OUTPUTS OF SAID PICKOFF MEANS; A SUBTRACTING MEANS CONNECTED TO EACH OF SAID PICKOFF MEANS FOR THE PURPOSE OF PROVIDING AN OUTPUT