Has anyone seen one of these? Mine seems to work fine, although it's not been calibrated for many years. I think it goes back to maybe 1962 or so.

The main voltage reference is temperature controlled in an oven. The unit is on three rack panels with cables connecting them.

That's pretty neat.

Super high-end stuff in its day, that's for sure.

Can you post some pictures of the internals? What are they using for a voltage reference? A zener diode or something else?

I never saw the reference. It's inside an oven.

It utilizes stepping switches, typically of the type in telephone exchange equipment. The AC unit has controls to adjust frequency response.

A manual for this is hard to find; I believe Tucker has one but I don't want to buy it. If anyone is interested in having this for his very own, I am open to reasonable offers. In comparison with my other 'accurate' meters, it seems to be very close in calibration. With 5 digits of resolution it's really a nice machine.