The marking went a little weird. Canvas doesn't seem to stretch much, but carefully marked with templates mated to their reflected shape were gaining or loosing a quarter inch or more when pinned from one end or the other. All this chasing and pulling of the edge itself distracted me for a seam or two from the ground rules of fabric, it usually stretches but seldom evenly. Point control using pins had gotten me trough walking fabric before, but hitting one is easy and several kinds of a drag. Starting at the ends and working in potential errors are absorbed through compression or stretch over the whole edge. I liked these clamps better than pins. No poking accidents, and they're easy to not sew over.