The present invention is a method for determining the center to center spacing of conductors in an insulated, multi-conductor, flat cable. The method comprising applying an X-ray field to the cable, detecting the X-ray field intensity that passes through the cable, obtaining a digitized output waveform of the X-ray field intensity as a function of cable position, and determining a trough location of the waveform by averaging calculated position values for the center of the conductor at several longitudinal positions along a cross section of the conductor.