This Standard establishes common terminology and gives guidelines for the description, principle of operation, selection, installation, and flow calibration of thermal dispersion flowmeters for the measurement of the mass flow rate, and to a lesser extent, the volumetric flow rate, of the flow of a fluid in a closed conduit. Multivariable versions additionally measure fluid temperature and static pressure. Thermal dispersion mass flowmeters are applicable to the flow of single-phase pure gases and gas mixtures of known composition and, less commonly, to single-phase liquids of known composition. This Standard applies only to fluid flow that is steady or varies only slowly with time.