Review on Accurate Repeated Measurement Corners by Cary Clemons

Very difficult to use. It seems like it would be better if I had three arms. With your left hand, hold the end of the tape on one side of the window, with your right hand, hold the tape spool in the air over the right side of the window, and with your third hand, move this tool along the tape at the end of the window sill. Due to the curvature of the blade of my tape measure, its end on the left window sill doesn't exactly fit the window sill. Without this tool, I can hold the tape and bend the right window sill, giving me fairly accurate measurements. Getting accurate measurements is a great idea, but you'll need to use an assistant to secure the blade or tape measure.