From time to time testing tubes on various testers I run into the same issue and was told not to trust or use a tube when it happens.

As an ex. testing nos 3at2 high voltage rectifier tubes and the tester says good if above 40 and most test about 55. I will have one that pegs the needle at 100 but is not shorted or gassy.

Well over the years I see this every once in a while with different number/function tubes. What causes this and was the advice given to me accurate about not using that tube?

What test are you performing?
On what tube-tester(s)?

ok lets see;

Testers jackson 648, tv7, Fair radio's computerized military " Card reader ", and Fair radio's solid state BK tube tester.

tubes, recently 3at2, 8hg8 and over the years a few others.

part of my job when I worked at Fair Radio was checking tubes for orders and once every 6 months or so I would have one that would act that way.

It was always an emissions test.

I've noticed that problem too and usually with NOS/unused tubes. I'll gauge them by turning the sensitivity back a little and noticing by how much. I generally still consider them to be a good tube if no other sysptoms are noted.

I believe that when the tester manufacturers were specifying the set ups/readings according to scale that maybe they "averaged" the settings?

ok thank you, this question was driving me nuts. I did notice just once that the tube in question would slowly drop down some if I left it sit on the tester for about an hour or so