When computing the volumetric flow of a gas in standard volume units (e.g. SCFM), the
equation becomes much more complex than the simple (flowing) volumetric rate equation. Any
equation computing flow in standard units must predict the effective expansion of the gas if it were
to transition from flowing conditions (the actual pressure and temperature it experiences flowing
through the pipe) to standard conditions (one atmosphere pressure at 60 degrees Fahrenheit). The
compensated gas flow measurement equation published by the American Gas Association (AGA
Report #3) in 1992 for orifice plates with flange taps calculates this expansion to standard conditions
with a series of factors accounting for flowing and standard (“base”) conditions, in addition to the
more common factors such as velocity of approach and gas expansion. Most of these factors are
represented in the AGA3 equation by different variables beginning with the letter F