User`s guide

Remarks
The dBm reference resistance is not reset when math functions are
enabled by the CALCulate:STATe command, nor when a
CALCulate:FUNCtion command is sent with CALCulate:STATe set to ON.
The dBm reference resistance value is stored in non-volatile memory. It is
not affected by a power-on cycle, Factory Reset (*RST command),
Instrument Preset (SYSTem:PRESet command), or function change.