The Measurement of Angles

We think of one of the arms of an angle as the initial line and the other as the bounding line.
The angle between the two lines is then measured by the amount of turning which is made by the bounding line
as it revolves about the point of intersection from coincidence with the initial line till it reaches its final position.
The positive direction of rotation is taken as that which is opposite to the motion of the hands of a watch.
The right angle has been taken as the unit of angle.