A flexible coupled‐cavity interferometer for student use has been constructed. A helium–neon laser serves as a source of radiation and as a phase‐sensitive detector of optical path changes. A phonograph turntable allows the convenient magnetic mounting of various reflecting components at varying linear velocities. Methods of calibration and possible laboratory measurements of transient events are discussed. [The apparatus described in this article was first prize winner in the College Intructional Laboratory category of the 1975 AAPT Apparatus Competition—Editor]