Electronic level

Claim 1

AN ELECTRONIC LEVELING INSTRUMENT COMPRISING A FRAME HAVING A LONGITUDINAL AXIS AND A REFERENCE SURFACE ADAPTED TO BE POSITIONED AGAINST A SURFACE THE DEVIATION OF WHICH FROM A DATUM PLANE IS DESIRED TO BE MEASURED; A HOUSING SUPPORTED IN SAID FRAME; A PENDULUM DISPOSED IN SAID HOUSING; MEANS FOR SUPPORTING SAID PENDULUM IN SAID HOUSING AND PERMITTING MOVEMENT OF SAID PENDULUM IN THE DIRECTION OF SAID LONGITUDINAL AXIS; A DIFFERENTIAL IMPEDANCE DEVICE MOUNTED IN SAID HOUSING ADJACENT TO, AND IN COOPERATIVE RELATION WITH, SAID PENDULUM, SAID DEVICE BEING ADAPTED TO PRODUCE AN OUTPUT SIGNAL IN RESPONSE TO LONGITUDINAL MOVEMENTS OF SAID PENDULUM ON EITHER SIDE OF A NULL POSITION CORRESPONDING TO THE TRUE VERTICAL POSITION OF THE PENDULUM; AND MEANS CONNECTED TO SAID PENDULUM FOR VARYING THE SIGNAL PRODUCED BY SAID IMPEDANCE DEVICE UPON LONGITUDINAL MOVEMENT OF SAID PENDULUM FROM SAID TRUE VERTICAL POSITION, SAID PENDULUM SUPPORTING MEANS COMPRISING A PAIR OF FLAT, FLEXIBLE, V-SHAPED MEMBERS ATTACHED TO AN UPPER PORTION OF SAID HOUSING AND DEPENDING THEREFROM IN LONGITUDINALLY SPACED RELATION, SAID MEMBERS HAVING ANGULARLY INTERSECTING LEGS OF EQUAL LENGTH WITH THE SPACED ENDS OF SAID LEGS DISPOSED UPWARDLY AND ATTACHED TO SAID HOUSING, SAID LEGS HAVING AN INTERSECTING PORTION ADJACENT SAID PENDULUM AND ATTACHED THERETO ALONG A LONGITUDINAL AXIS PASSING SUBSTANTIALLY THROUGH THE CENTER OF GRAVITY OF SAID PENDULUM, WHEREBY TRANSVERSE TILTING OF SAID FRAME AT ANGLES LESS THAN ONE-HALF THE INCLUDED ANGLE OF SAID ANGULARLY INTERSECTING LEGS HAS MINIMAL EFFECT ON THE LONGITUDINAL MOVEMENT OF SAID PENDULUM AND THE ACCURACY OF SAID LEVELING INSTRUMENT.