Abstract: A measuring device that employs interference optics for detecting and tracking the movement of a mechanical element (4) has a light source (31) for emitting a light bundle that is capable of interference, a diffraction grating and a sensor arrangement (33). A beam path leads from the light source to the sensor arrangement (33) by way of the diffraction grating (32). The diffraction grating divides the light bundle into at least three partial components, thereby forming a light patch having three overlapping maxima, the center, zero maximum and the two minus one and plus one maxima on either side, at the optical sensor arrangement (33). The light beams for generating the three brightness maxima interfere with one another, so the resulting superposed light patch (46) contains interference bands that run in one direction or another when the diffraction grating is moved. The movement of the interference bands is detected with the sensor arrangement (33), and evaluated in an evaluation circuit.