Patent ID: 7450246

Claim:
A measuring apparatus for determining relative positions of a positioning stage moveable in at least one direction (X, Y) within a predeterminable maximum traversing path, comprising: at least one interferometric measuring device; and, at least one interferometric correction device, wherein measuring results for determining relative positions of the positioning stage for a movement along a movement direction are generated by the at least one interferometric measuring device, wherein the at least one interferometric measuring device is operable with laser light of a laser of at least one wavelength, wherein correction results are generated with the at least one interferometric correction device, wherein said interferometric correction device is arranged to determine an actual wavelength of the laser light during a position determination of the positioning stage in order to correct for a variation of the wavelength of the laser light when evaluating the measuring results, and wherein the interferometric correction device is proximate to the interferometric measuring device and the proximity corresponds to a predeterminable portion of the maximum traversing path of the positioning stage.