I bought the Curve Master at an annual quilt show and couldn't quite get the hang of it, so stopped back at his booth next year. He immediately knew my problem; I was not holding the top piece straight enough up in the air. Sure enough, that fixed my curves. I can never remember concave , convex, in, out, pout, smile, just top and bottom. Good luck. I will admit I've had just as good of luck with pinning and going slowly.