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Procedures for precision polishing and testing spheres of silicon and silica are described. Hand-polishing procedures result in the production of spheres of 90 mm diameter with deviations from roundness of less than 50 nm. The roundness was measured to an uncertainty of 5 nm on a Talyrond with averaging procedures to account for spindle errors.
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Leistner et al. (1991) studied this question.
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