Volumetric measurement is the measurement of liquid volumes. Volumetric measurement includes measurement made through positive displacement (PD), turbine, sonic nozzle, vortex shedding, mass flow and other types of meters. We will not cover the measurement of product in gaseous (vapour) state.
It also includes measurement by static volumetric measures. Calibration of volumetric metering systems is usually done through comparisons to a standard volumetric prover vessel or by series flow through a pipe or piston prover. In the case of a Mass Flow Meter (Coriolis Effect Mass Meter) with mass output, proving may be accomplished by mass to mass comparison using a weigh scale of known performance. If a mass flow meter is expected to display volume, then the situation is slightly more complex.
Much of the calibration of volumetric measures is done using water as the medium. This is done for various reasons including safety, ease of obtaining the product and the well know characteristics of water. Calibrations done using water are often referred to as a "water draw". To use water as a transfer medium, you often need to know the density of water. While most of us assume water has a density of 1 kg = 1 litre, this is not exactly true. Water density changes with temperature and with purity. As it turns out, even the purity of the water can become an issue for some calibrations. At a minimum, distilled water will be required in order to remove any impurities. More information than you probably ever wanted to know about water is also available in the discussions on Vienna Standard Mean Ocean Water or VSMOW.
A PDF copy of the Wagenbreth & Blanke densities from 0.01° Celsius to 40° Celsius in 0.01° increments, is available from APLJaK Ventures.