This was my great find at Spring 2010 Quilt Market in Minneapolis. This ruler has a "channel" that locks onto the seam allowance. No turntable or repositioning required. It totally eliminates ruler rock. As the advertising states, "Perfect Results Every Time!!!"
I never did like squareing up my half-square triangles. I found it easier to cut them at ?? and 7/8", sew and press. Were they always the correct size? No, but just as close as I could get using a "rocking ruler". I love these rulers. I have them on order, I will announce when they arrive in the shop.