I have a Bernina Activa 240 with a #37-1/4 inch foot. I just measured about 2 days ago and it sews a perfect 1/4th inch. Maybe the discrepancy between all of our 1/4-inch measurements is the difference in how all the models of Bernina's sew???
I really didn't like mine at first...thought it was a little persnickity...but now that I'm used to it, I love it.