A CO2laser interferometer and fringe counter, made of commercially available equipment, which can resolve displacements of 5 &mgr;m and accurately track velocities of up to 50 m/s in either a positive or negative sense, is described. Coupled to a heterodyne interferometer, this simple fringe‐counting circuit does not require exact quadrature to determine the direction of motion, is wideband and capable of high count rates (dc—10 MHz) and will not introduce false fringe counts at phase reversal or due to dithering of the target. A prototype has been built and employed to characterize the operation of a pulsed gas valve.