Modern valve testers

[Sparks]

I would imagine that modern valve testers are limited to a few of the most popular valves used in amplifiers, but would not be suitable for more obscure types.    Having only had a valve tester for a few weeks, it took ages to acceot the fact that it was working OK.    But the results don't really make much sense to me because some valves that I know work very well, are showing very poor, and hardly any are going well up into the green.     I am still investigating testing valves, but only from a practical point of view, not having any great interest in theory beyond the most basic elements.     I would really like to evolve something that gives me an accurate picture of what condition a valve is in.     Not asking for suggestions here, because I now have sufficent clues to proceed.
Bob
PS Saw two mercury vapour rectifiers on the car boot sale this morning, but gave them a miss after recalling one or two of them exploding in the public address system of a passenger ship many years ago!