Pointer locking mechanisms for exposure meters and the like

Claim 1

A METER INCLUDING A HOUSING, AN INDICATOR AND AN INSTRUMENT MOVEMENT MOUNTED IN SAID HOUSING AND COUPLED TO SAID INDICATOR, SAID MOVEMENT BEING RESPONSIVE TO A MEASURED PARAMETER FOR CAUSING CORRESPONDING MOVEMENT OF SAID INDICATOR, FIRST AND SECOND MEMBERS MOUNTED IN SPACED-APART RELATIONSHIP FOR RECEIVING THEREBETWEEN A PORTION OF SAID INDICATOR, THE FIRST MEMBER MOUNTED FOR MOVEMENT IN THE GENERAL DIRECTION OF MOVEMENT OF SAID INDICATOR TO RESPECTIVE FIRST AND SECOND POSITIONS AND THE SECOND MEMBER MOUNTED FOR MOVEMENT INTO AND OUT OF RESTRAINING ENGAGEMENT WITH SAID INDICATOR, AND MEANS COUPLING SAID FIRST AND SECOND MEMBERS FOR DRIVINGG SAID SECOND MEMBER FROM RESTRAINING ENGAGEMENT WITH SAID INDICATOR WHEN SAID FIRST MEMBER IS MOVED TO THE SECOND POSITION, WHEREIN THE IMPROVEMENT COMPRISES; A DEVICE MOUNTED FOR SLIDABLE MOVEMENT ON SAID HOUSING IN DIRECTIONS TRANSVERSE TO THE DIRECTION OF MOVEMENT OF SAID INDICATOR AND HAVING PORTIONS THEREOF WHICH PROJECT INTERIORLY AND EXTERIORLY OF SAID HOUSING, A CAM LOBE FORMED ON THE INTERIOR PORTION OF SAID DEVICE FOR DRIVING SAID FIRST MEMBER FROM SAID FIRST AND SECOND POSITION WHEN SAID DEVICE IS MOVED A GIVEN DISTANCE IN ONE DIRECTION, SAID CAM LOBE RETAINING SAID FIRST MEMBER IN SAID SECOND POSITION UNTIL SAID DEVICE IS MOVED A GIVEN DISTANCE IN A DIECTION OPPOSITE SAID ONE DIRECTION, SAID CAM LOBE COMPRISING TWO STEPS SURFACES LYING IN PLANES SUSTANTIALLY PERPENDICULAR TO THE DIRECTIONS OF MOVEMENT OF SAID FIRST MEMBER AND A RAMP SURFACE JOINING SAID TWO STEP SURFACES AND LYING IN A PLANE INCLINED IN SAID DIRECTION OPPOSITE SAID ONE DIRECTION OF DEVICE MOVEMENT.