Agilent Technologies EPM-P Series Programming Manual page 180

• If the last measurement on either channel is not valid error -230, "Data
corrupt or stale" occurs. A measurement is valid after it has been
initiated. It becomes invalid when either a reset occurs or any
measurement parameter, for example frequency, is changed.
• If the expected_value and resolution parameters are not the same as
the current expected value and resolution settings on the specified
window, error -221, "Settings conflict" occurs.
EPM-P Series Power Meters Programming Guide
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FETCh[1]|2|3|4[:SCALar][:POWer:AC]:DIFFerence:RELative?
[<expected_value>[,<resolution>[,<source list>]]]
Measurement Commands
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