This Standard applies only to ultrasonic flowmeters that base their operation on the measurement of transit times of acoustic signals. Further, this Standard concerns only the application of such meters when used to measure the volumetric flow rate of a liquid exhibiting homogeneous acoustic properties and flowing in a completely filled closed conduit. Not covered by this Standard are ultrasonic flowmeters that derive volumetric flow rate from measurements of the deviation, scattering (Doppler flowmeter), or correlation of acoustic signals. This Standard provides: (a) a description of the operating principles employed by the ultrasonic flowmeters covered in this Standard; (b) a description of error sources and performance verification procedures; (c) a common set of terminology, symbols, definitions, and specifications.