A new ‘diffractographic’ technique for measuring displacements has been developed which uses changes in the diffraction pattern of a single slit aperture formed between a fixed edge and an edge of the member itself. Described herein is an extension of the method whereby two diffraction patterns representing states of beam deflection produce moiré-type fringes of proportional spacing. Both ‘live-fringe’ and double-exposure diffractograms are shown to form these fringes and the resulting patterns directly depict deflection to within ± 0.0001 in all along the beam, over a displacement range of at least 0.1 in.
