The above figure is an example of a 90 degree clockwise rotation, denoted as R_{(0,0),90}. A rotation is a rigid motion that rotates, or turns, a pre-image around a fixed point. When rotating a shape, all segment lengths and angle measures are preserved. Each point on the pre-image and its corresponding point on the image are equidistant to the center of rotation. The proper way to write out a rotation is R_{(center of rotation),(degree of rotation)}. Any clockwise rotation must have the degree of rotation represented by a negative value. On a coordinate plane, the rule for rotating any point 90 degrees counterclockwise (or 270 degrees clockwise) is (x,y) -> (-y,x). The rule for rotating any point 180 degrees is (x,y) -> (-x,-y). The rule for rotating any point 270 degrees counterclockwise (or 90 degrees clockwise) is (y,-x).