Presser feet can help you achieve a 1/4" seam allowance, but there are other variables...feed dogs, flatness of the machine before the fabic goes under the needle, the size of the needle, stitch length, how you hold the fabric, etc... that also affect getting a precise measurement that you may want to check as well. I find it much easier to simply mark where I need to have the fabric placed before it goes under the presser foot and use a wood kabob skewer to guide it as it goes under the foot and hold the fabric straight. People use a lot of different methods to mark where the fabric needs to be placed. I think they even make gizmos to do that too.