Electrical clamp-on meter with swivel connected tongs

Claim 1

AN ALTERNATING CURRENT MEASURING INSTRUMENT, COMPRISING A COMBINED CASING AND HAND-GRIP UNIT AND A HEAD UNIT, THE HEAD UNIT INCLUDING AN INDUCTION COIL AND A MAGNETIC CORE STRUCTURE THROUGH SAID COIL, SAID MAGNETIC CORE STRUCTURE INCLUDING A PAIR OF TONGS RELATIVELY MOVABLE BETWEEN OPEN AND CLOSED POSITIONS FOR ENCIRCLING A TEST CONDUCTOR, SAID CASING AND HAND-GRIP UNIT CONTAINING AN ALTERNATING CURRENT MEASURING CIRCUIT CONNECTED TO SAID COIL AND RESPONSIVE TO THE CURRENT FLOW IN THE TEST CONDUCTOR, SAID MEASURING CIRCUIT INCLUDING AN ELECTRICAL INDICATING METER, A SWIVEL CONNECTION BETWEEN SAID HEAD UNIT AND SAID COMBINED CASING AND HAND-GRIP UNIT, AND MANUAL OPERATING MEANS FOR SAID TONGS INCLUDING SPRING MEANS NORMALLY BIASING THE TONGS CLOSED, A TRIGGER MOVABLY MOUNTED IN SAID COMBINED UNIT, AND MECHANICAL COUPLING MEANS BETWEEN SAID TONGS AND SAID TRIGGER FOR PROVIDING AN OPERATING CONNECTION FROM SAID TRIGGER TO SAID TONGS FOR OPENING THE TONGS AGAINST THE BIAS OF SAID SPRING MEANS DESPITE SWIVEL MOVEMENT OF SAID HEAD UNIT RELATIVE TO SAID COMBINED CASING AND HAND-GRIP UNIT.