Light & easy-to-read stainless-steel squares can additionally serve as angles of inclination & try squares. The blades are exactly 15 mm wide, the standard measurement in Japan for tenons & board thicknesses. The front of the square has the usual deep-etched metric markings (mm). The back of the square has two special calibrations: one gives the circumference of a measured diameter (x 3.14) & the other the length of one side of a square inscribed by that circumference (x 0.7).