Abstract: An encoder disc for a photoelectric shaft angle encoder includes a disc body which defines first and second regions. The first region is defined between two circles of differing radii and offset centers positioned such that the two circles are substantially tangent at one point and the smaller circle is contained within the larger circle. The second region is situated adjacent to the first region, and the first and second regions have differing light transmission characteristics. The first region forms a measuring track which varies in width substantially sinusoidally around the disc body. Especially good results are obtained when the two circles are offset from the central axis of the disc body by substantially equal amounts.