Amprobe ACD-6-PRO Clamp-On-Multimeters - Manual (Page 5)

4
4) OPERATION
DC Voltage and AC Voltage functions
Inputs are made through the test lead terminals.
Note: DC 400.0mV range is designed with 1000M Ω high input impedance for least
current drain in measuring small signals, and can cope better with most commercially
available voltage output transducers/adapters. The non-zero display reading is normal
when the meter inputs are open circuit, which will not affect actual measurement
accuracy. The meter will show a close to zero reading when the inputs are shorted.
Open input is actually a floating condition, which is not a zero-volt-input condition.
Note: AC 400.0mV range selection is by RANGE button manually, and is specified from
AC 40mV & up for ACD-6 Pro and from AC 60mV & up for True RMS model ACD-6
TRMS Pro.