ASTM D4172 for wear preventive characteristics of lubricating fluid (Four-ball method)
11. Precision and Bias
NOTE 4 - The precision data were derived from cooperative testing by 13 laboratories on 5 oils under the conditions listed in Section 7. A description of the oils and the average of wear scars obtained at each of the two testing conditions on each of the oils are shown in the Appendix.
11.1 The precision of this test method as determined by the statistical examination of interlaboratory test results is as follows:
11.1.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following value only in one case in twenty:
Repeatability = 0.12 mm scar diameter difference
11.1.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, exceed the following value only in one case in twenty:
Reproducibility = 0.28 mm scar diameter difference
11.2 Bias - The procedure in this test method has no bias because the value of ball scar width can only be defined in terms of a test method.
12. Keywords
12.1 lubricant; wear
