Test limits using correlated measurements

In the standard model for inspection of manufactured parts measurements of the characteristic of interest are subject to, typically small, measurement errors. This leads to test limits which are slightly more strict than the corresponding specification limits. Quite often, however, such direct measurements are quite expensive, and it would be worthwhile to be able to use cheaper measurements on some strongly related characteristic. Therefore recently derived accurate methods for setting test limits are extended in this paper to cover the case of such correlated measurements. It is demonstrated how such limits can be compared in terms of costs to the earlier obtained limits based on direct measurements.