The most common method of surface evaluation in optical production uses optical test plates. The main objections to test plates concern the possibility of damage to the surface through contact and the need for a different test plate for every different surface. A surface measuring interferometer is described which is capable of measuring the radius of curvature and the surface irregularity independently. The process of evaluating surface irregularity is simplified since all power error can be nulled out. Other useful applications of the interferometer are also described.