1. A method of calibrating the thermal trip setting of a thermalmagnetic trip mechanism utilized in an electric circuit breaker, wherein the trip mechanism includes a bimetallic element deflectable in response to overload current through the circuit breaker, an electromagnet mounted by the bimetallic element and responsive to high magnitude fault current levels for attracting an armature, movement of the armature unlatching the circuit breaker operating mechanism to trip the circuit breaker, an armature stop for establishing the quiescent position of the armature, and a hook mounted by the metallic element and having a tip for engaging and moving the armature to trip the circuit breaker upon deflection of the bimetallic element in response to sustained overload current levels, said method comprising the steps of: A. placing the trip mechanism in a fixture with the paRts thereof assuming relative positions identical to the relative positions they would normally assume in an operative circuit breaker; B. referencing the fixture in a predetermined fixed spatial position; and C. machining away a portion of a particular part of the trip mechanism so as to establish a predetermined operative positional relationship between the hook and the armature when positioned against the armature stop.