A position measurement system configured to measure a position quantity of a movable object in a measurement direction, the system including a radiation source, a beam splitter to split the radiation beam in a measurement beam and a reference beam, a first reflective surface mounted on the movable object to receive the measurement beam, a second reflective surface mounted on a reference object to receive the reference beam, and a detector arranged to receive a first and second reflected beam reflected by the first and second reflective surface, respectively, and configured to provide a signal representative of the position quantity of the movable object based on the first and the second beam, wherein the radiation source and detector are mounted on an object that is different from the movable object and the reference object.