Remote electronic flow computers installed on orifice meters calculate, as part of their audit data trail, averages of the variable flow parameters (Pf - flowing pressure, hw - differential pressure, Tf - flowing temperature) for each time interval defined by the flow computer. Because of the interdependency of the flow parameters within the AGA-3 gas flow equation, the volume produced by applying that equation to the averaged parameters can often be significantly different from the sum of the instantaneous volumes calculated by the flow computer using the same equation. Because of this calculation-induced volume shift, averaged flow parameters should not be used to recalculate the volumes produced by flow computers unless the averages have first been adjusted to reproduce the summated volume for the time interval in question.

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