In this paper a grazing interferometry for measuring the flatness of non-optical surfaces is described. Many different surfaces have been examined

ranging from groundglass and photographic emulsions to metals such as steel

brass and aluminium

etc. The sensitivity of the measurement is such that one interference fringe represens a change of one half of the grating periodicity in height on the surface under examination. The visibility of interferogram can be improved by a suitable choice of gratings of different diffraction efficiency

or the grating orders.The interferometer is relatively easy to set-up and stable once aligned.