As far as reading the numbers and matching goes,
I believe thay have to be tested on the same tester to match do to the calibration of the tester.
I think that different brands of testers have their own rating tables as far as a bad, good and tests as new.
I'm sure that other members here with more experience than I will be posting soon to help you.
As stated in previous post, microphonics will show up if used in a preamp. A tube can test as new, but have very bad microphonics. Try and buy from someone that actually tests for that if buying tubes for your pre, I learned the hard way!
