Agilent Technologies U1251A User's And Service Manual page 157

Specifications 8
These specifications apply when using the U1251A and
U1252A handheld digital multimeter in an environment that
is free of electromagnetic interference and electrostatic
charge.
When using the multimeter in an environment where
electromagnetic interference or significant electrostatic
charge is present, measurement accuracy may be reduced.
Agilent U1251A/U1252A User's and Service Guide 157