This James Taylor video makes me think I see why my friend's tuning appears to be flat according to my tuners. It is quite possible his tuning fork sets him minus 10ish and he goes from there and all notes are indeed MINUS according to my tuners but sound right to him. I finally see the rationale.
Plug your guitar into a tuner pedal, then strike and hold his tuning fork over the pickup. It will produce a big fat signal that will let you see how far off the fork is.
