Abstract: A tachometer particularly adapted for operation as a rotational velocity feedback transducer is provided. First and second proximity detectors are used to monitor orthogonal positions of an irregular surface portion of a rotating shaft and provide x and y signals that are substantially in quadrature. The x and y signals are differentiated with respect to time to provide differential signals that are representative of dx/dt and dy/dt, respectively. Signals representative of products x dy/dt and y dx/dt are generated from the x signal and the differential signal dy/dt, and the y signal and the differential signal dx/dt, respectively. A signal representative of algebraic sum x dy/dt--y dx/dt is generated from the signals representative of products x dy/dt and y dx/dt. A signal representative of quotient of (x dy/dt-y dx/dt) divided by the displacement r.sup.