Abstract: The invention relates to an improvement for a wafer mounting table particularly for use in photolithographic apparatus for processing wafers comprising a compact mounting block made of glass-ceramics which has two neighboring back supports limiting two sides of a top face of said mounting block. The top face is provided with at least three studs for supporting a wafer to be processed. The sides of the back-supports facing away from said top face are provided with an elongated horizontally extending silvered area each, which is in opposition to a laser path measuring system each. The laser beams of said laser path measuring system define a plane which coincides with a projection plane of a projection lens being provided in opposition to a wafer mounted on said studs. Means are provided for substantially eliminating departures of the silvered areas from a straight plane. Further means are provided which enable a quick adaption of the laser mount for wafer charges having different thicknesses or diameters.