rt pivots the clockwise (Right Turn).
The turn is measured in degrees.
rt 90
Notice that the turtle will not actually move in the new direction
until you tell it to move forward with fd.
When using a pen, putting rt between two fd moves can draw an angle.
pen purple fd 100 rt 120 fd 100
Notice that the angle used by rt is the exterior angle.
The interior angle added to the exterior angle will be 180.
For example, the 60 degree interior angle drawn by the program
above corresponds to the 120 degree exterior angle swept out by
the turtle.
`rt can also be used to draw curves by using a second argument. Read the reference page on curves.