Holography has two facets which make it a revolutionary scientific instrumenta-tion technique. The first capability is that holography can be used to circumvent photography's depth-of-focus problem for small objects in motion. The second is that measurements equal, equivalent, or beyond those of an interferometer can be made with the technique. The latter can be done in terms of two holograms recorded on the same photographic plate (double-exposed holographic interferometry),lin terms of holograms on separate plates, or in terms of comparing the reconstruction from a hologram against the actual scene wavefront at a later time (stored beam holographic inter-ferometry). 2 In each case, the difference in phase between the two light wave patterns produce fringes, with each fringe tracing the loci of constant phase or equal optical path length. Neighboring fringes are normally separated by an optical path length of one full wavelength:3,4,5 The new ability to make optical interferometric measurements on and in hitherto impossible situations is an extremely valuable contribution. Of particular value are measurements on diffuse surfaces, which are impossible with classical interferometry.