ASTM D4212 Standard Test Method for Viscosity by Dip-Type Viscosity Cups
12. Report
12.1 Report the efflux time to the nearest 0.2 s for Zahn or Shell cup No. ___, manufactured by ___, (in the case of Zahn cups) the temperature of the fluid (where measured), and whether the result is from a single measurement or the mean of two of more measurements.
13. Precision and Bias
13.1 The most satisfactory results when using dip cups are obtained when viscosity is being controlled at a single location only. However, when comparisons between locations are made, cups from the same manufacturer must be used or other action taken to ensure compatibility of results. The following criteria can be used for judging the acceptability of results at the 95 % confidence level:
13.1.1 Zahn Cups - Precision was determined on the basis of an interlaboratory test in which six laboratories used new Zahn cups (all from the same set from the same manufacturer) to test eight paints covering a broad range of viscosities. The within-laboratory coefficient of variation was 3.7 % and the between-laboratories coefficient of variation was 11.5 %. Based on these coefficients the following criteria should be used for judging the acceptability of results at the 95 % confidence level:
13.1.1.1 Repeatability - Two results, each the mean of two measurements, obtained by the same operator should be considered suspect if they differ by more than 11 % of their mean value.
13.1.1.2 Reproducibility - Two results, each the mean of two measurements, obtained by operators in different laboratories should be considered suspect if they differ by more than 33 % of their mean value.
NOTE 6 - The values used to determine the precision were obtained under ideal conditions (a single set of cups), reproducibility in practice can be just as good, by employing strict controls and good techniques.
13.1.1.3 Bias - Bias does not apply to this test method as no acceptable standards exist.
NOTE 7 - Since the precision values were obtained under ideal conditions (a single set of cups), reproducibility in practice probably is poorer than that given (perhaps as bad as 50 %).
13.1.2 Shell Cups - Precision was determined on the basis of an interlaboratory test in which four laboratories tested seven paints covering a broad range of viscosities. The within-laboratory coefficient of variation was 3.2 % and the between-laboratories coefficient of variation was 6.3 %. Based on these coefficients the following criteria should be used for judging the acceptability of results at the 95 % confidence level:
13.1.2.1 Repeatability - Two results, each the mean of two measurements, obtained by the same operator should be considered suspect if they differ by more than 9 % of their mean value.
13.1.2.2 Reproducibility - Two results, each the mean of two measurements, obtained by operators in different laboratories should be considered suspect if they differ by more than 18 % of their mean value.
13.1.2.3 Bias - Bias does not apply to this test method as no acceptable standards exist.
14. Keywords
14.1 dip cup(s); flow cup(s); Shell cup(s); viscosity; Zahn cup(s)
