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

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## Circles, Measurement Of

The measurement of circles is closely connected to the measurement of angles. This is because the measurement has a rotational aspect; that is, one ray must be turned about the vertex until it coincides with a more static aspect. The circle is the perfect tool for measuring **planes** of angles, because any angle cuts off the same fractional part of every circle whose center is at the vertex of the angle.

## Different Ways to Measure Circles

In degree measure, the circle is divided into 360 equal parts, while in **gradient** measure, 400 equal parts of a circle are used. Since there are four right angles in a circle, there are 100 gradients in a right angle, making gradients a better fit with the decimal system. Nevertheless, degree measure is the predominant system for measuring angles using fractional parts of a circle.

A different method for measuring angles...

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