By contrast, most onsite viscometers measure dynamic viscosity, but are programmed to estimate and report kinematic viscosity, so that the viscosity measurements reported reflect kinematic numbers reported by most labs and lube oil suppliers.

Most used oil analysis laboratories measure and report kinematic viscosity. The two are easily confused, but are significantly different. Viscosity can be measured and reported as dynamic (absolute) viscosity or as kinematic viscosity. However, there is more to viscosity than meets the eye. Likewise, there is no property more critical to effective component lubrication than base oil viscosity. Of all the tests employed for used oil analysis, none provides better test repeatability or consistency than viscosity.

Viscosity reporting is only valid when the temperature at which the test was conducted also is reported - for example 23 cSt at 40 degrees C. This value is converted to standard units such as centistokes (cSt) or square millimeters per second. It is determined by measuring the time in seconds, required for a fixed volume of fluid to flow a known distance by gravity through a capillary within a calibrated viscometer at a closely controlled temperature. Kinematic viscosity is a measure of a fluid's internal resistance to flow under gravitational forces.