[Phlogiston]

The ohms per volts is usually included in the calibration instructions. As a rule, the earlier the instrument or radio you are working on, the lower (and hence more "loading" of the item you are measuring) the ohms per volt rating specified for the VM required. 

Since we are on the subject, I would like to recommend to all of you an instrument that a good bud gave me a year ago. It is a military AN/USM 223 Multimeter. One of the neat features it offers is the option of 1000 ohms per volt OR 20 thousand ohms per volt for DC measurements.   






Yep.

I have 2 or 3 nice VTVMs. I think the last one I was using was not isolated from the line. Dumb. Don't remember the ohms/volt on it.

Really the best for caling the old tube testers would be the 80s model Archer (radio shack) I keep at home to check such thing as AA batteries, replaced at the shop with the big $$ Fluke.