Well…
That sucks.
I can’t find a service manual for the 820…odd that they included meter cal trimmers for the 812 but I see in pics it’s blanked off for the 820.
The manual includes no specifications regarding the meter specs that I can find, relative level (like what the numbers on the scale actually mean). We can *assume* “0” is -10dBv, but we don’t really know for sure. And beyond that are they averaging or peaking etc. so maybe your meters don’t need calibrating, we just need to know more about them. If everything sounds fine go with that first, it’s just unfortunate you don’t have the benefit of the useful functionality of the meters, but in your case at least their function is duplicated by the ADAT meters. If you want to check what the scale means or determine if you need to or want to go further with exploring the potential of calibrating your meters, if you have a signal generator and a good audio meter, set your tone generator to produce a 1kHz sine wave tone, connect that to your group 1 BUSS IN jack on the Fostex via a ‘Y’ cable, and to the unterminated leg of the ‘Y’ cable connect your level meter. Set the level of the 1kHz tone to 316mV AC. Now move the level meter to the group 1 output jack and adjust the group 1 fader until your level meter reads 316mV AC at the group 1 output jack. Now look at the group 1 meter. What does it display? If you do this test, repeat it for groups 2 through 8 and report back.