Natural gas measurement today is accomplished through the use of two different classifications of gas meters. The first
consists of inferential type meters, including, orifice, ultra-sonic and turbine meters, and the second is the positive
displacement meters, which consist of diaphragm and rotary displacement meters. The inferential type meters are so-called
because rather than measuring the actual volume of gas passing through them, they “infer” the volume by measuring some
other aspect of the gas flow and calculating the volume based on the measurements. The positive displacement type meters
are so-called because they measure the actual volume of gas displaced through them.