The present disclosure relates to a photolithography system having an ambulatory projection and/or detection gratings that provide for high quality height measurements without the use of an air gauge. In some embodiments, the photolithography system has a level sensor having a projection source that generates a measurement beam that is provided to a semiconductor substrate via a projection grating. A detector is positioned to receive a measurement beam reflected from the semiconductor substrate via a detection grating. An ambulatory element selectively varies an orientation of the projection grating and/or the detection grating to improve the measurement of the level sensor. By selectively varying an orientation of the projection and/or detection gratings, erroneous measurements of the level sensor can be eliminated.