US Patent 7621056 Ruler

A ruler in which one pair of parallel cuts are put in one raw material plate, a supporting point part is formed by narrowing both ends of the parallel cuts or making the both ends like a fork, a bent cut or a linear cut reaching to an end part of the raw material plate is put so as to surround the supporting point part or extend along it, and an arch part, in which a part included between the parallel cuts is bulged upward by heating, pressure friction, injection molding or chemical treating, is formed monolithically with the raw material plate, or made one in which a slip stop is applied wholly or partially in a back face of the arch part.