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MATHEMATICS FOR AIR CREW TRAINEES   38

The following table of angular measurement shows the symbols used for these units of angular measurement:

360° (degrees) = 1 circumference

1° = 1/360 part of a circumference

60' (minutes) = 1°
60''(seconds) = 1'

Only the degree is used in this manual.

b. An angle is the figure formed by drawing two straight lines outward from a common point. The common point is called the vertex of the angle and the straight lines are called the sides of the angle. in figure 38, O is the vertex and NO and PO are the sides of the angle NOP. Another definition of an angle is the amount of rotation or turned necessary to rotate NO to the new position PO. The air navigation system of measuring them in degrees clockwise from the north through 360°. This angle is sometimes referred to as azimuth.

[[image - drawing of a angle identifying the vertex O, the base of the angle and P and N, the arms of the angle]]
FIGURE 38.

c. The instrument for measuring angles is the protractor. To measure an angle with a protractor, place the protractor on the angle to be measured (see fig. 39) so that either half of the side AB will fall up on one side of the angle and the point O on the vertex. The reading on the scale where the other side of the angle crosses it is the measure of the angle in degrees.

[[image - drawing of a protractor]]
FIGURE 398.


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