Minimum allowed drop on ac voltage

RoyB mentioned that he uses the plugin analog AC voltmeter, one must remember that this meter sometimes needs to be set or calibrated with a known good voltage source. I have one but the MH bounces so much that it goes out of calibration occasionally . When I arrive at my destination and set up and hook up shore power I get the Fluke out and match it to the meter. You use the small slotted screwdriver in the slot at the bottom of the meter to match voltage. Digital voltmeters are much nicer, but are much more expensive. JMT