Abstract: A device for measuring the rotation of a member includes an angular error sensor having a movable sensor element connected to the rotatable member and a pair of guadrature-spaced stationary elements for inducing the error in the sensor element. A detector measures the polarity and amplitude of the error and delivers it to a processor that accumulates successive error signals. The accumulated signal is averaged, corrected and displayed as the measurement. Also the accumulated signal is used to control a set of multiplier devices that create different driving signals from a single signal source for application to the guadrature elements of the error sensor. The output of these multiplier devices is controlled by the processor such that the error signal is driven toward zero.