Abstract: An optic displacement sensor includes first and second optic circuits which optic circuits include bi-directional means for a light supply path to and a light return path from a light reflecting surface means. The first optic circuit is a reference signal circuit, and the second optic circuit is a measuring signal circuit. Means are provided for directing light into the light supply paths for the pair of optic circuits, and means are provided whereby the light from the light supply paths of the pair of optic circuits is received by light reflecting means and at least partially reflected into the light return paths where it is detected. Further, the sensor includes means for adjusting the detected signal from one of the light return paths with respect to the detected light from the other light return path.