These require a laboratory to do duplicate tests on some of their own samples, and to use the results to check that they can achieve similar repeatability to that shown in the histograms of ranges in the reports of the cross-testing experiments. In this context, a "duplicate test" consists of testing two test portions of the same laboratory sample under repeatability conditions. About fifteen duplicate tests are needed to allow a reliable assessment of a laboratory's repeatability.
A likely reason for poor repeatability is inexperience on the part of an operator. Repeatability checks should therefore be seen as an important part of the training an operator receives when he is learning to perform a test.
Test results for repeatability checks should be rounded to no more than 0.5 times the repeatability standard deviation.
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