To maintain a 1/4" seam on my 6600, I move my needle to the 6.0 spot. To determine this, I drew a 1/4" line from the edge of a piece of paper, I then put it up to the guide on the foot and moved the needle until it was just inside the line. Try that with your machines. then put a post a note on your machine with the number you come up with so that you don't forget.