The DIN ISO 2909-2004 standard specifies the test method and calculation formula for calculating the viscosity index of petroleum products by kinematic viscosity. The standard is applicable to the mass evaluation of transparent and opaque petroleum-based oils, especially lubricating oils. The viscosity index is an important indicator to characterize the performance of oil viscosity with temperature changes. This standard calculates the viscosity index by giving the kinematic viscosity value at two temperatures, providing a unified basis for the production, quality control and performance optimization of lubricating oils. The content of the standard specifies the test steps, formulas and scope of application to ensure the accuracy and conformity of the calculated results.