Abstract: A digital tachometer having an optical sensor which provides a signal at a frequency related to the rotational or reciprocating speed of a moving object, a phase locked loop and a frequency divider circuit connected for operation as a frequency multiplier to be responsive to the sensor signal to provide a serial pulse train the period of which is an integral multiple of the sensor signal, a pulse accumulator for registering the pulses and a time rate generator which enables the pulse accumulator to register pulses for a preset duration so that the number of pulses registered is a direct representation of the revolutions per minute of the moving object.