The development of a data acquisition system for a high resolution motion analyzer is discussed. The displacement measurement is based on a Michelson-type heterodyne interlerometer. The gained detector signals of the interferometer are processed by the direct phase comparison method. This method makes it possible to achieve a resolution equivalent of 1/512 of the applied optical wavelength, without the intricate signal conditioning needed by the commonly used phase-locked loop frequency multiplication or analog signal multiplication methods. The main technical data of the system are 1.25-nm resolution, 20-m measuring distance, and 60-kHz sample rate. The accuracy is better than ± 10 nm ± 0.1 ppm within a velocity range of ± 1.8 m/s and an acceleration range of ± 9900 m/s2.