5.1 Knowledge of the average fiber length and the distribution of fibers is of primary importance to users of top in further processing.

5.2 Acceptance specifications for the fiber length and length distribution may be established by the user based on the type of yarn-making equipment employed and the desired end uses.

5.3 Test Method D519 for testing wool top for fiber length is considered satisfactory for acceptance testing of commercial shipments since the method has been used extensively in the trade for acceptance testing and the current estimates of the between-laboratory precisions are acceptable.

5.3.1 In case of a dispute arising from differences in reported test results when using this test method for acceptance testing of commercial shipments, the purchaser and the supplier should conduct comparative testing to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens that are as homogenous as possible and that are from a lot of the type material in question. The test specimens should then be assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using Student's t-test for unpaired data and an acceptable probability level chosen by the two parties before testing is begun. If a bias is found either its cause must be found and corrected or the purchaser and supplier must agree to interpret future test results in the light of the known bias.

FIG. 1 Wool Fiber Stapling ApparatusTABLE 1 Form with Recorded Data Showing the Calculation of the Average Fiber Length of Wool, the Standard Deviation, and Coefficient of Variation Note 1-When using equipment graduated in metric units, use class intervals 10 mm long, and calculate the average and standard deviation to the nearest 0.2 mm.

B = the largest midpoint value for which a frequency is recorded = 6.25 in.

m = the class interval = 0.5 in.

Percentage of fibers under 2 in. = 39.0 %.

Calculations:

v = 100 (σ/X) = 100 × (1.4/2.6) = 56.47 %.