This chapter deals with the primary elements currently available for measuring gas flow. This includes orifices@ venturi tubes@ flow nozzles@ rotameters. swirlmeters@ anemometers@ and the like. Each produces a measurable phenomenon. such as a pressure drop@ that can be correlated to gas flow. Although such auxiliary or secondary equipment as gages@ manometers@ transmitters@ and the like are not treated herein@ a discussion of these can be found in other texts.1* This chapter also covers the application of less direct methods of flow rate determination@ such as stoichiometric calculations@ fan performance curves@ and tracer gas dilution. A special effort has been made to indicate the best areas of application of each indirect method or primary device mentioned. *REFERENCE on page 4-14.