The photo-electric method for measuring the hairiness of yarns is not recommended for acceptance testing of commercial shipments since experience has shown that results obtained from machines produced by one manufacturer cannot usually be verified by machines produced by another manufacturer. This guide is intended to increase the awareness of the user to available techniques for measuring hairiness. In some cases the purchaser and the supplier may have to test a commercial shipment of one or more specific materials by the best available guide though it has not been recommended for acceptance testing of commercial shipments.

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, test samples that are as homogenous as possible, drawn from the material from which the disparate test results were obtained, and 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.

There may be a distinct difference in testing speed and tension devices of machines supplied by different manufacturers that may give differences in reported test results.

The measurement of hairiness is important to yarn producers. This guide is useful for process control and research of the yarn surface design at an individual manufacturing facility. Hairiness also is used to provide yarn processing machine design, and indications of malfunctioning process equipment, such as rotors, doffing mechanisms, guides, and travelers. It can be used to identify some causes of barreness and shade variation in fabrics.