Position measuring device

An apparatus comprising:

• a fine-positioning table;
• a coarse-positioning table;
• a position measuring device, comprising:
• a reflective scale that is disposed in a stationary fashion,
• a scanning unit disposed on said fine-positioning table, which positions said scanning unit relative to said reflective scale in a measuring direction, said scanning unit comprising a retroreflector;
• and:
• a signal unit disposed on said coarse-positioning table, which positions said signal unit in said measuring direction, said signal unit comprising a light source and a detector arrangement, wherein said scanning unit and said signal unit are structurally separate from one another and are disposed in planes parallel to one another, and wherein said scanning unit is movable relative to said reflective scale in a measuring direction, and
• said light source emits a beam that propagates freely in a direction to said scanning unit, wherein from said scanning unit along said direction to said signal unit a pair of interfering partial beams propagate freely and wherein between said signal unit and said scanning unit said partial beams propagate freely in a propagation direction that is oriented perpendicular to said planes.