No need to draw pencil lines! Since you have to trim the corner anyway, why not trim it first, and use the raw edge as your seam guide? AND... Since the corner was trimmed with a straight edge, your bonus triangle is ready to sew into a Half-Square-Triangle Block!
And, use the 45 degree angle to create binding or mitered corners. The Folded Corner Clipper comes with fully illustrated step by step instructions.
The ruler slides easily over the fabric until pressure is applied. Then, our exclusive gripper holds the fabric in place while cutting, eliminating slipping and miss-cuts!