Investigation into the Accuracy of Industrial Measurement of Sizes between 0.02 Inch and 5 Inches

Abstract

The system of limits and fits introduced by the ISA, covering the size range 0.04 in. up to 5 in., is now being revised by the International Organization for Standardization and will include an enlarged section on measuring instruments because of their much wider adoption since the system was introduced in 1941. The British Standards Institution, who have been taking part in this revision, asked the National Physical Laboratory to investigate the current accuracy of industrial measurements in this size range. Work-pieces were therefore circulated to forty firms whose measurements were compared with those made at the N.P.L. The algebraic mean error of these measurements at different diameters, although having a distinctive pattern, was small in relation to the spread of individual errors about this mean. Errors on external measurements were less than those on internal measurements, and the report discusses this and other characteristics in relation to the techniques of measurement used. Some optimism is apparent in the estimates of accuracy made by the participating firms. The results of this investigation are linked with those of an earlier investigation covering the size range 4 to 80 in.