Most steel squares are heavy and awkward to use, but this slim Japanese square is light (3 1/2 oz) and flexible.
The thin, pliable stock and tongue, combined with the bevelled profile, allow you to hold it anywhere on the tongue and force the edge flat to the work for easy, accurate measuring. The corner is much thicker for rigidity.
The arms are 10 1/2" by 20 1/2", graduated in Imperial measure (inches) on one face and metric measure on the other face. It has large numerals and etched, black-filled markings for wear resistance and legibility.
Square to within 0.1mm per 100mm, it is made from hardened stainless steel. A well-made, convenient tool for layout.