1. Type the arc radius into the options tool bar and choose the arc
   direction (clockwise or counter-clockwise) and the solution (larger arc or
   smaller arc).
2. Specify the start point of the arc.
3. Specify the end point of the arc. If the end point is too far away from
   the start point for a solution, the closest solution is drawn (a half circle
   with the given radius and direction).
