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My colleagues and I are having somewhat of a debate on what flow units we should be using. We are using differential pressure transmitters to determine the flow of combustion air through a line. The temperature and pressure are being measured at the flow element and being inputted along with the DP meter to a PLC. The PLC then does a calculation to compensate for the actual pressure and temperature. The result of the calculation is then displayed on a screen as SCFM. It is my thought that the raw signal from the DP meter (square root is done at the DP meter) is SCFM based on the "standard temperature and pressure" that the flow element was tested at. These "standards" usually come from the data sheet that come with the flow element. Since the temp and pressure may vary, we measure them and continually compensate our flow measurement to determine the actual flow under the "non-standard" conditions and should express this flow as ACFM. Is this thought correct? Should the flow indication that is compensated using the actual(dynamic) temp and press be expressed as SCFM or ACFM??