Remarks
Use the [SENSe:]VOLTage:AC:NULL:VALue command to set the null value.
The CONFigure[:VOLTage]:AC and MEASure[:VOLTage]:AC? commands
turn off the null state.
A Factory Reset (*RST command) or an Instrument Preset
(SYSTem:PRESet command) returns the null state to off.
