ASTM D2270 for calculating viscosity index from kinematic viscosity at 40 and 100°C
7. Report
7.1 Report the viscosity index to the nearest whole number. When the number is exactly halfway between the nearest two whole numbers, round to the nearest even number.
7.2 Calculated viscosity index numbers can differ depending on the kinematic viscosity data as determined. When duplicate kinematic viscosity data are available, it is recommended that viscosity index values calculated therefrom be considered acceptable only when the kinematic viscosity data meet the acceptability limits in Test Method D445 of 0.35 % for repeatability and 0.70 % for reproducibility. It is also recommended that the viscosity index calculated and reported be that based on the means of the appropriate kinematic viscosity values. If the kinematic viscosity data do not meet acceptability limits in Test Method D445, the data should be examined and redetermined.
8. Precision and Bias
8.1 The calculation of viscosity index from kinematic viscosities at 40 and 100°C is exact, and no precision limits can be assigned to this calculation.
8.2 The accuracy of the calculated viscosity index is dependent only on the accuracy of the original viscosity determination. Test Method D445 has a stated repeatability limit of 0.35 % and a reproducibility limit of 0.70 %.
8.3 See Appendix X1 for a discussion of the precision that can be attributed to the viscosity index.
8.4 Bias - The calculation of viscosity index from kinematic viscosities at 40 and 100°C is exact, and no bias can be assigned to this calculation.
9. Keywords
9.1 kinematic viscosity; viscosity index
