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Concept

Three-plate method

Three concentric circular plates are stacked, with the innermost plate slightly offset, demonstrating a three-plate method concept for creating a flat reference surface through sequential grinding.

A bootstrap procedure for producing a truly flat reference surface without a flatter reference to copy from. Three iron plates are ground in rotation, A against B, B against C, then C against A; only when all three pairs make full contact everywhere can all three be plane, because any consistent curvature on one would force a complementary error in the others. The technique predates Maudslay but he formalised it for industrial use.

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