(, Plat.
. p. 51 C; , Arist.
. 14), a square, used by carpenters, masons, and
other artificers, to make their work rectangular (Vitr.
7.3; Plin. Nat. 36.172). It
was made by taking three flat wooden rulers [REGULA] of equal thickness, one of them being 2 feet
10 inches long, the others (called ancones,Vitr. 8.6) each 2 feet long, and joining them
together by their extremities so as to assume the form of a right-angled
triangle. (Isid.

Orig. 19.18.) 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 in woodcut at Vol. I. p.
429. 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,
found at Rome and published by Gruter (p. 229), and copied in the woodcut
which is here introduced.

The square was used in making the semicircular striae of Ionic columns [COLUMNA], a method founded on
the proposition in Euclid, that the angle contained in a semicircle is a
right angle (Vitr. 3.5.14).

From the use of this instrument a right angle was also called a normal angle. (Quint.
Inst. 11.3, p. 446, ed. Spalding.) Any thing misshapen was called
abnormis. (Hor. Sat. 2.2, 3.)

A rather more elaborate norma made of iron is preserved in the Museum at
Zurich. It has another leg added at right angles to the long side of the
triangle at one end of it, so that angles of 45°, 90°, and
135° can be measured. (Blümner,