Also just noticed I've never set the date on my camera...
I would guess that you are either measuring dynamic range, or playing with an ND filter.
Doing AFMA on my 5d4. It front focuses. My 70-200 needed plus 4 on the wide end and plus 8 on the long end. The old 6d needs no adjustment so this was a surprise. I need to do my 35mm now.
AFMA adjustments. I would have expected multiple exposures at a given setting, and then averaging the results.
I have found the “Dot Tune Method” on YouTube to be pretty effective, because it seems to eliminate the guesswork.