Omnigrid 12.5 " Square RulerIncludes diagonal angle and an extra 12 for seam allowances. Use to cut over sized squares, large rectangles, borders over 6, for checking finished size or alignment of sewn seams, cutting and checking large 45 triangles or even as a portable light table. Made of strong and durable premium quality acrylic plastic. Unique black and yellow double sight lines for easy viewing when working with light and dark fabrics. Laser cut to within 0. 002 accuracy