User`s guide

Description
This command returns the current power-line reference frequency used by
the 34410A/11A/L4411A analog-to-digital converter. You can set this
reference frequency with the CALibration:LFRequency command. Normally,
when you apply power to the instrument, the instrument automatically
detects the power-line frequency (50 Hz, 60 Hz, or 400 Hz) and uses this
value to determine the integration time used.