User`s guide

Remarks
The reference frequency used by the 34410A/11A/L4411A analog-to-
digital converter is based on the power line frequency measured at power
on. But, the reference frequency is set to either 50 Hz (for a power line
frequency of 50 Hz or 400 Hz), or 60 Hz (for a 60 Hz power line
frequency). The CALibration:LFRequency? command returns the reference
frequency (+50 or +60). The CALibration:LFRequency:ACTual? command
measures and returns the actual power line frequency.
This command does the same thing as the SYSTem:LFRequency:ACTual?
command.