Abstract: A shaft synchronous balancing apparatus wherein a rotor to be balanced is rotated in conjunction with appropriate balance plane located transducers and a non-contacting shaft monitoring pick-up, for example of an optical variety. The latter pick-up derives a one times per revolution reference signal which is treated by a software driven process control system including dual timer-counters to evaluate the period of revolution, T, and to develop N incremental sampling pulses having a duration or time constant of T/N. Preferably, N is an even integer power of 2. Periodic updating of the duration of a time constant is developed utilizing only one software interrupt in conjunction with the two counter timers. A nulling technique for canceling offset at the signal treatment stages is provided which accommodates for the high amplification levels necessary at the front end of the system.