Abstract: A two-pole miniature circuit breaker is configured for calibration of both pole mechanisms with the circuit breaker fully assembled. The identical pole mechanisms are mounted in the same orientation in parallel outer compartments of a molded housing with the metal support frame of one pole against the outer housing wall and the frame of the other spaced from the associated outer wall. A coupler couples the two-pole mechanisms together for simultaneous opening of both poles when either pole is tripped has an actuating member on each end which engages the trip device of the associated pole. The actuating member, at least of the pole with the metal frame spaced from the housing outer wall, is configured to provide direct access for a calibration tool inserted through a calibration opening in the housing to engage a calibration slot in the metal frame.