I work a lot with high voltages and others frequently replicate ... It’s for use with a 10MΩ +/-1.0% voltmeter, or oscilloscope as in the photos above. Meters with other impedances can be ...

It stands for vacuum tube voltmeter. At first glance ... have a FET front end and probably uses a MOSFET. That means the voltage measurement probes don’t really connect to the meter at all.