I teach a Beginning Piecing Workshop regularly. I teach my students that all seams in piecing are a scant 1/4". And, that everyone finds their scant 1/4" seam differently. I have them sew on a 1/4" graph paper to see where the edge of the paper hits when they are sewing just to the right side of the line on the graph paper. When I sit down to my machine, I bump the needle bar position over one notch to the right, and guide the edge of my fabric just inside the feed dogs. 2 students in my current class, bump their seam allowance over 2 notches, but have to use the regular presser foot instead of a quarter-inch foot. Some can do great with guiding the fabric along the quarter-inch foot, but most can't see the right side edge of that foot. Here's a picture of sewing on graph paper to find that scant 1/4".