User`s guide

Remarks
This command affects dc voltage measurements only.
With "AUTO OFF" (default), the input impedance for dc voltage
measurements is fixed at 10 MΩ for all ranges.
With "AUTO ON", the input impedance for dc voltage measurements is
automatically selected according to range. The impedance is set to "HI-Z"
(>10 GΩ) for the 100 mV, 1 V, and 10 V ranges. The 100 V and 1000 V
ranges remain at a 10 MΩ input impedance.
The CONFigure and MEASure? commands automatically select "AUTO OFF"
(fixed at 10 MΩ for all ranges).
This setting is reset to the default (fixed, 10 MΩ) by the *RST and
SYSTem:PRESet commands.