I know what you mean. The seller seem to assume that you have (or at least know the specifics of) his particular tester and its numerical values, not to mention its quirks and nuances. Also, some tube testers, such as my Eico 667, have multple settings for the same tube type, depending on whether you use the integral roll chart or the various printed charts and whether you test for 12AX7 or ECC83 (supposedly identical). I have a "choice" when I test my 12AX7s, for instance, and you can bet I'd be tempted to pick the one that shows the tubes in the best light. Not that I'd EVER give in to such temptation, you understand :-)
Dave
Dave