1. Choose the direction of the arc in the options toolbar.
2. Set the center of the arc using the mouse or enter a coordinate in the
   command line.
3. Define the radius by clicking a point on the arc or by entering a
   coordinate into the command line. You may also enter the radius in
   the command line.
4. Set the start angle with the mouse or by entering a coordinate or the
   angle in the command line.
5. Set the end angle the same way as the start angle.
