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A new interferometer for calibration of graduated line scales is described. It uses a novel method for observation of the distance between the graduation lines. The line images are recorded by a moving microscope and a CCD camera. A frame-grabber unit is used to digitize the images. We calculated the position of the microscope at the moment of charging the video fields by the use of digitized interference and video-synchronization signals. For elimination of the effect of carriage rotations, the focus point of the microscope and the apex of the main-arm cube-corner reflector are adjusted to the same point. The measurement and the analysis processes are completely automated. The estimated overall uncertainty (1σ) for a 1-m Invar scale is 44 nm.
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Lassila et al. (1994) studied this question.
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