Abstract: A position measuring system includes for the determination of a reference position at least one additional reference scanning unit which is shiftable relative to the measuring scale, independently of the measuring scanning unit and the measuring scale, and accordingly of the machine components connected to the measuring scanning unit and the measuring scale. The measuring scale carries an incremental graduation and a reference mark, and the measuring scanning unit and the reference scanning unit carry indicator blocks which on coincidence form a zero indicator. In order to determine the reference position, the reference marks and the zero indicator are scanned successively, but in arbitrary sequence, and their differential spacing is determined with the aid of a graduation of the reference scanning unit.