During an opening or closing operation, the moving contact of a circuit breaker travels a few centimetres in a few tens of milliseconds. A transducer coupled to the mechanism records that position instant by instant and produces the travel curve, the mechanical signature of the operation.
From the curve come the parameters that actually define the state of the mechanism: total stroke, the velocity over the contact separation segment — which determines whether the arc is properly quenched — overtravel, bounce and the behaviour of the damper at the end of the run.
This is what separates a basic breaker analyzer from a complete one. A timing set tells you whether the operation took as long as it should; the travel curve also tells you why, and lets you spot a tired spring or a spent damper before the timing drifts out of tolerance.