This Standard, provides information on the use of multiport averaging Pitot head-type devices used to measure liquids and gases. The Standard applies when the conduits are full and the flow (a) has a fully developed profile; (b) remains subsonic throughout the measurement section; (c) is steady or varies only slowly with time; (d) is considered single-phase. A differential pressure transmitter or other pressure measuring device, known as a secondary element, must be used with a multiport averaging Pitot primary element to produce a flow rate measurement. Although multiport averaging Pitot primary elements are sometimes used in noncircular conduits, such applications are beyond the scope of this Standard.