14. Precision and Bias
14.1 Precision - The precision of this test method with CCS-2B (manual) as determined by the statistical examination of the interlaboratory test results over the temperature range from -5 to -30°C and viscosity range from 1560 to 10 200 mPa•s is as follows:
14.1.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test materials would, in the long run, in the normal and correct operation of this test method, exceed the following values only in one case in twenty.
repeatability = 5.4 % of their mean
14.1.2 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 values only in one case in twenty:
reproducibility = 8.9 % of their mean
14.2 Precision - The precision of this test method with CCS-4/5 (automatic) as determined by statistical examination of the interlaboratory test over the temperature range from -10 to -35°C and a viscosity range from 2800 to 18 000 mPa•s, using version 4.x or higher software, is as follows:
14.2.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test materials would, in the long run, in the normal and correct operation of this test method, exceed the following values only in one case in twenty.
repeatability = 2.6 % of their mean
14.2.2 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 values only in one case in twenty:
reproducibility = 7.3 % of their mean
14.2.3 Summary of Interlaboratory Study - The interlaboratory study consisted of nine participating laboratories evaluating ten engine oils with viscosities ranging from 2800 to 18 000 mPa(s) at test temperatures from -10 to -35°C. All laboratories used the CCS 4/5 with version 4.x or higher instrument software to measure the apparent viscosity.
14.3 Bias - The procedure in this test method for measuring the apparent viscosity of engine oils at low temperatures has no bias because the apparent viscosity of engine oils at low temperature is defined only in terms of this test method.
14.4 Automated Precision - The automated CCS and automatic automated CCS viscometers have been found not to have a bias from the manual CCS2 viscometers, and the precision is within the precision of the manual apparatus.
15. Keywords
15.1 apparent viscosity; cold cranking; cranking; engine oils; petroleum and petroleum products; viscosity
