Some quarter inch foots have a fabric guide that feeds the fabric in correctly. Well, I say correctly, but I've never measured my seams to see if it is a true quarter inch. Like someone said, it doesn't matter so much if you are consistant. I say that, but then you may have trouble with your square rulers to square it up. Example, a 12 1/2 inch ruler might be too big if your block is only 12 inches.