This method is considered satisfactory for acceptance grading of commercial shipments because it has been used extensively in the trade for this purpose.

6.1.1 If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if there is a statistical bias between them, using competent statistical assistance. As a minimum, use the samples for such a comparative tests that are as homogeneous as possible, drawn from the same lot of material as the samples that resulted in disparate results during initial testing and randomly assigned in equal numbers to each laboratory. The test results from the laboratories involved should be compared using a statistical test for unpaired data, a probability level chosen prior to the testing series. If a bias is found, either its cause must be found and corrected, or future test results for that material must be adjusted in consideration of the known bias.

The appearance of a woven or knitted fabric depends to a large extent on the smoothness, cleanliness, and general appearance of the yarns from which the fabric is manufactured. Instruments are available for the measurement of unevenness and for counting neps and other imperfections in yarn, but the values obtained from such tests are not easily integrated into an over-all expression for actual fabric appearance. Yarn appearance grading affords additional information which the manufacturer of woven or knitted goods may, through experience, correlate with the appearance to be expected in fabrics made from the yarns.