ASTM D2270 for calculating viscosity index from kinematic viscosity at 40 and 100°C
4. Significance and Use
4.1 The viscosity index is a widely used and accepted measure of the variation in kinematic viscosity due to changes in the temperature of a petroleum product between 40 and 100°C.
4.2 A higher viscosity index indicates a smaller decrease in kinematic viscosity with increasing temperature of the lubricant.
4.3 The viscosity index is used in practice as a single number indicating temperature dependence of kinematic viscosity.
