I have two Mamiya m645's and I know the focus is off on the one I use. It's been a long time since I used it and now that I have replaced the seals and cleaned it up I can't remember which way I turned the lens to correct for the focus being off. I was too lazy back then and just ran a roll of film and took exposures with the focus "on, a little to the left, and a little to the right" It wasn't much to figure out which way and then I got it right all the time.

It uses a lot of film to adjust and reshoot and adjust and reshoot to get it adjusted. I thought about putting a ground glass on the film plane with the insert out, focusing and then adjusting the screen to match.

Anyone have a better or correct way to do it?