In this paper, a simple method is described for the measurement of small angles of rotation of a flat surface using a circular optical grating, which may be generated and projected onto the test surface using either a standard Michelson interferometer or a computer-controlled LCD projector. In view of its availability in most laboratories, a Michelson interferometer is used in this paper. The diameter of the grating that is generated can be easily magnified or be reduced to suit the size of the test surface. With circular grating, the angular rotation of both diffuse and specularly reflective surfaces about any axis of rotation can be measured from the distortion of the grating. The distorted grating that is diffracted from a specularly reflective surface may be recorded in two different ways using a CCD camera. In the first method, the distorted grating is recorded off the mirror surface as though it were a diffuse surface. In the second method, the distorted grating is specularly reflected onto an opaque screen and the CCD camera subsequently records the grating image off this screen.