ClipArt ETC
"A square used by carpenters, masons, and other artificers to make their work rectangular. It was made by taking three flat wooden rulers of equal thickness, one of them being two feet ten inches long, the others each two feet long, and joining them together by their extremities, so as to assume the form of a right-angled triangle. This method, though only a close approximation, must have been quite sufficient for all common purposes. For the sake of convenience, the longest side, i. e. the hypotenuse of the triangle, was discarded, and the instrument then assumed the form in which it is exhibited, among other tools, on a tomb found at Rome, and which resembles that in modern use. A square of a still more simple fashion made by merely cutting a rectangular piece out of a board is shown on another sepulchral monument and copied in the woodcut which is here introduced." — Smith, 1873

Norma

"A square used by carpenters, masons, and other artificers to make their work rectangular. It was made…