Abstract: A system for determining the cumulative position and periodic average velocity of a rotating body having an incremental encoder, operatively connected to the body, for generating a series of periodic signals indicative of rotation of the body. The system also includes a high frequency clock for generating clock pulses at a frequency greater than the maximum frequency of the encoder signal, and a timer for controlling the total time of a predetermined sample interval. Also included in the device is a counter for accumulating the number of integral encoder signal cycles that have been completed, an arithmetic logic unit for determining the size of a fractional portion of an encoder signal cycle that was completed between the last integral encoder cycle and the end of the sample interval.