The relationship of the length of a piece of fabric and the length of yarn in the fabric can be determined accurately only be measuring the length of yarn entering the loom and the length of fabric made from that particular length of yarn. In most cases, however, the determination must of necessity be made on a woven fabric by measuring the length of yarn removed from a measured length of fabric, thus introducing certain variations that will influence the accuracy of the test. Yarn removed from the woven fabric contains undulations or waves that have been introduced by the weaving process. Heat, moisture, and mechanical shrinkage on subsequent finishing operations may accentuate these undulations, and in all probability, increase the force to pull them out and straighten the yarn. In order to accurately measure the length of the yarn after the removal of the crimp, these undulations must be pulled out without elongating the yarn. In some cases, the minimum force necessary to straighten the yarn will cause a certain amount of the elongation to take place, thus increasing the length of the yarn. Also, stresses imposed upon the yarn during the weaving process may have been sufficient to stretch the yarn beyond its elastic limit, again increasing its length. It is recognized that determination made by measuring length of yarn removed from a measured length of fabric may tend to give crimp values that are somewhat higher than the crimp in the yarn as it lay in the fabric. In the case of fabrics made from yarns that exhibit differential shrinkage, or yarns of widely different count, or yarns woven at different tensions, the crimp of each type of yarn in the fabric must be determined and reported separately.

This test method can be used for acceptance testing of commercial shipments but comparisons should be made with caution because information on estimates of between-laboratory precision is limited as noted in 13.1.

If there are differences of practical significance between reported test results for two laboratories (or more), comparative tests should be performed to determine if their is a statistical bias between them, using competent statistical assistance. As a minimum, ensure the test samples to be used are as homogeneous as possible, are drawn from the material from which the disparate test results were obtained, and are randomly assigned in equal numbers to each laboratory for testing. The test results from the two laboratories should be compared using a statistical test for unpaired data, at 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.