Abstract: A position sensor has a scale consisting of tracks of indicia in the form of bar patterns acting on a detector having a two-dimensional array of sensitive elements. One track has indicia with a pitch slightly greater than the pitch of the sensitive elements and another track has indicia with a pitch slightly less than the pitch of the sensitive elements. The other tracks provide a coarse determination of the position of the scale relative to the detector while the first two tracks provide resolution of the position to less than the pitch of the sensitive elements. There is sufficient redundant information to enable accurate position detection even if there are optical or electrical perturbations in the detection of individual indicia.