Square Squared Half Inch Ruler (9 1/2" by 16") ~from Studio 180 Designs

The Square Squared Half Inch is an all-in-one tool that gives you a window template for accurately cutting the center square, a chart printed right on the ruler for the recommended size to cut the triangles sewn to the four sides of the center square, and a trim down section on the ruler that simplifies the alignment of the ruler to fabric unit and allows everyone to clean up the unit to a precise measurement every time.