Abstract
The need to formulate proposals for the extension of the I.S.A. system of Limits and Fits above 500 mm. (20 inches) has required an improved knowledge of the accuracy of industrial measurement of such sizes. In an investigation conducted by the National Physical Laboratory (N.P.L.) this information has been obtained for diameters up to 2,000 mm. (79 inches) from a number of firms who have made measurements upon a special set of work-pieces circulated amongst them, these measurements being compared with those made at the N.P.L.
The industrial measurements tended to be too small, especially at the larger diameters. Both this tendency, expressed as the algebraic means of the measurements, and their standard deviation about this mean, bore an approximately linear relationship with diameter in this range of size. Supplementary information on measuring equipment did not suggest that, among the techniques more commonly used, there was one which provided particularly accurate results, but indicated that some refinement in existing equipment and methods could do much to improve accuracy of measurement.
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