If you asked them to produce it, out would come a familiar item, a handheld brick with a 7-segment LCD at the top, a chunky rotary selector switch, and a pair of test probes.

Plug the other end of each cable into the matching-color binding post. Turn on the multimeter, move its selector dial to the voltmeter function, and set the range to 20 volts. Turn on the SPST switch.