A variable inverse period timer computes the inverse period between events, where the repetition frequency of the events can vary greatly. Where the repetition frequency of the events is relatively high the average inverse period of a plurality of events is computed, and where the repetition frequency of the events is relatively low a single inverse period is computed. This is accomplished by providing a digital differential analyzer which generates the locus of possible inverse periods from an initial condition and which is activated a fixed time after the occurrence of a first event. Upon occurrence of an event subsequent to the activation of the digital differential analyzer, the value generated by the digital differential analyzer is essentially multiplied by the number of events which occurred since the first event.