*Macmillan Science Library: Mathematics*. Copyright © 2001-2006 by Macmillan Reference USA, an imprint of the Gale Group. All rights reserved.

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## Early Measurements of Angles

Ancient civilizations were first concerned with measuring right angles, because of the importance of right angles in the construction of buildings and in surveying. Early instruments for measuring right angles included tools resembling the modern carpenter's square, the baculum (sometimes called the geometric cross or cross-staff), and a rope stretched to form a 3-4-5 right triangle.

The baculum consisted of a flat rod approximately 4 feet in length with a cross-piece that could be slid along the rod while remaining always **perpendicular** to it. The idea of stretching a rope into the form of a known figure, such as the 3-4-5 right triangle was immortalized by the Egyptian "rope-stretchers."

The concept of measuring angles other than right angles requires some consistent unit of measure. Sometimes that unit angle appears to have been the right angle, as in the ancient Greek's use of...

This section contains 1,486 words(approx. 5 pages at 300 words per page) |