I found it is hard to get repeatable readings for 6dj8 tube. When I use 15000 scale, the reading is too sensitive to English position. Every step represent about 500 on the reading. I don't know if I have a bad English.
Each hash mark on the 15000 scale represents 250 Micromhos
I am still confusing about 6922 vs 6dj8. I can get over 10000 reading for some 6922 tube.
That sounds like you are not setting the ENGLISH knob at the correct RED dot on the ENGLISH dial. The RED dot you should be using is the one that has 15000 printed just below it.
6922 ( Hickok 600A tube settings and Mutual Conductance readings.)
6.3 EV-7608-0 27 90 P4 6500 Triode #1. R
6.3 EV-2103-0 27 90 P4 6500 Triode #2.
Mutual Conductance/ Micromhos 6500.
If you are setting all the knobs correctly and you are still reading 10000 Micromhos for a 6922 then there must be a problem with the supposedly calibrated tester.
How are the 9 pin tube socket connection tension of the tube socket? Fairly tight or loose fitting?
The ENGLISH Control ganged two pots may be dirty. You might try rotating the dial back and forth several times around the area of the 15000 scale RED dot.