Viscosity is a measure of a liquid's flow properties. This information is used for blending oils; determining the spray (nozzle) characteristics of oil burners and diesel fuels; defining a product's lubricating properties and predicting how a mixture of oils and other products will dry, protect, spread, etc.
In kinematic viscosity testing, the sample is allowed to reach test temperature and is then passed through a glass capillary (Ubbelohde). The efflux time is multiplied by a capillary-specific calibration factor and reported as viscosity. The liquid's "viscosity index" is calculated by determining its viscosity at two or more temperature points and applying a standard algebraic equation to the data. Viscosity index is an important characteristic of modern lubricating oils.