Keysight Technologies 3458A Guide D'utilisation page 91

Configuring for Measurements 3
Figure 3-4 4-Wire ohms measurement connections
Configuring the A/D converter
The A/D converter's configuration determines the measurement speed, resolution,
[1]
accuracy, and normal mode rejection for DC or ohms measurements. The
factors that affect the A/D converter's configuration are the reference frequency,
the specified integration time, and the specified resolution.
The reference frequency
When power is applied, the multimeter measures the power line frequency,
rounds the value to 50 Hz or 60 Hz, and sets the A/D converter's reference
frequency to the rounded value. (For a 400 Hz power line frequency, the
multimeter uses 50 Hz as the reference frequency, which is a subharmonic of
400 Hz.) For DC or ohms measurements, the multimeter achieves normal mode
rejection (NMR) for noise at the reference frequency when the integration time is
≥1 power line cycle. See Setting the integration time (following) for more
information.
[1] Normal mode rejection (NMR) is the multimeter's ability to reject noise at the power line frequency
from DC or ohms measurements.
Keysight 3458A User's Guide 91