Note:  Do not rely on this information. It is very old.


Angle between two lines, the amount of rotation required to bring a line from one position to the other, regard being taken of the "sense" or direction which the bounding lines are understood to possess. If two lines are parallel and drawn in the same sense no rotation is necessary, hence the angle between them is zero. Angles are measured in (a) Sexagesimal measure. A complete rotation is called four right angles.

1 right angle = 00 degrees ().

1 degree = 60 minutes (').

1 minute = 60 seconds (").

(b) Centesimal measure.

1 right angle = 100 grades (gr.).

1 grade = 100 French minutes (').

1 Fr. min. = 100 French seconds (").

(c) Circular measure. By the ratio of the circular arc subtended by the angle to the radius of the arc, a ratio found to be constant for any ratio if the angle is constant.