The Phase-Shift Indicator is a high-quality accessory designed to measure the rotor phase angle of the Three-Phase Synchronous Motor/Generator, Model 8507. It consists of a transparent plastic disc calibrated in electrical degrees and a metal mounting bracket. It attaches to the end of the machine carriage with slide fasteners. The rotor phase angle can be read by illuminating the end of the machine shaft, through the calibrated disc, with a Stroboscope, Model 8922. The reading corresponds to the phase angle, in electrical degrees, of a four-pole ac machine.