The exact equivalent of the western carpenter's framing square and used for exactly the same purpose. In fact they have to be very accurate, because if the carpenter's square is 'out' then the whole building is going to be 'out'. However, unlike western framing squares these are light and flexible. The cross section of the arms shows a bevel on each edge allowing the square to be tilted when marking out, bringing the graduations closer to the workpiece, minimising errors caused by parallax. This bevel also helped prevent ink from smudging when the Japanese carpenter drew a line or, more importantly, it kept the marking knife's edge from damaging the square. The arms are graduated in centimetres and millimetres. Interestingly the reverse of the long arm has a scale for determining the maximum size of a square beam obtainable from a round log, simply by placing the scale across the diameter and taking the measurement.