Shown is a vintage Thomson AC voltmeter manufactured by General Electric sometime between 1895 and 1909. The device on the top of the meter is a resistance, most likely a wire wound type. I was a little skeptical about testing this meter, so I plugged it into my variac and slowly increased the voltage. As old as this meter is, it read the voltage perfectly. It's reading exactly 120 volts. It's also quite heavy and well made.