An experimental gross motion analysis technique is described for determination of the relative motion between two bodies moving in two or three dimensions. A light-emitting diode mounted on each body is photographed in stereo by a high-speed camera. The digitized data are manipulated by several computer subroutines to yield the three-dimensional relative motion between the two bodies. Output is displayed on a graphics terminal. This instrumentation is utilized for analyzing spatial linkages; planar high speed mechanisms, where the reference variable is time. 40 refs.