A characteristic of all liquids is that a change in volume occurs with a change in temperature. This thermal coefficient of expansion varies with each liquid. The measurement of most liquids is based on net volume, defined as volume at a referenced base temperature (60 degrees F for the petroleum industry in the U.S.A. for example). When metering liquids, the operating temperature is usually other than the base temperature and can also vary during the measurement. The difference between gross metered volume and net volume will depend on the coefficient of expansion of the liquid and the difference between average metered liquid temperature and base temperature.
Meters equipped with the ATC Automatic Temperature Compensator provide net volume or weight registration. This registration is based on continuous integration of gross metered volume and temperature regardless of flow rate and temperature fluctuations. It is also based on the coefficient of expansion of the particular liquid being metered.