What you want to know without having a meter plugged into the power line all the time. Well here's a fun project.
A variac is the best method to do this of course.
Take two or three Neon bulbs NE2 and build a box to put them in, drill 4 holes, two for the light bulbs and two for the 100 K ohm potentiometers.
One potentiometer is adjusted to come on when the line voltage is too High, say 127 Vac the other is adjusted to light up at any voltage you think is above the minimum voltage you want to be alerted to. Of course you will have to make sure your pots will handle at least 1/4 watt or more.
Put each pot in series with each bulb. the end of the neon should be connected to one side of the line and the connected pot should go to the other side of the line. I would also add a safety resistor to prevent the bulb from shorting out. Be sure to insulate everything.
Bulb a will light if the voltage exceeds 110 volts
Bulb b will light if the voltage exceeds 122 volts
And if you wish add a 3rd bulb with fixed resistor to indicate power is on.
You use a multimeter to adjust the voltage across the pot to make the light just turn on at the lowest voltage you desire.
make a power connection and no more guessing if the line voltage is too low or High.
No need to monitor a meter that way.
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