[turretslug]

Come to think of it, as well as a few 100k/V meters, there were also various 50k/V multimeters on the hobbyist market from the likes of Jemco, Eagle and Micronta that could be used with a commercial or home-made probe for low loading. It can get difficult to transfer absolute traceability for high voltages with the same confidence as low voltage- but as mentioned, HV generators and circuitry have high impedance, so circuit voltages are usually either approximately right, or way off kilter.

As mentioned by Andy, there's also the option of a divider probe into a DMM- there'll be plenty of guidance on this and other forums,

Colin