A degree is defined as a complete rotation in either a clockwise direction or anticlockwise direction, where the starting and the ending point are the same. The rotation is dissected into 360 units.
Let's consider a circle of radius one unit. Also, the arc of the circle is one unit. The measure of the angle is 1 radian if the arc subtends at the center of the circle, given the radius and arc lengths are equal. The arc length of a circle with radius unity is equivalent to the angle in radian.
A grade can be described as a right angle split into a hundred (100) equal parts. Further, each grade is dissected into a hundred minutes and each minute into a hundred seconds.