Abstract: A method and an apparatus for a precision optical distance measuring device which can be used to determine both external and internal target geometries. The beam from a frequency modulated laser diode is split into reference and target beams. A closed loop control system modulates the amplitude of the reference beam to maintain a balance between the power in the target return beam and the reference beam. This enables the sensor to operate with targets of widely varying reflectivity and across a broad range of angles of incidence of the target beam to the target. The reference and target return beams interfere at a detector producing a beat wave. The beat frequency is linearly related to the distance of the target from the sensor. The frequency of the beat wave is determined to high precision, thus giving the position to high precision.