3-Point arc
The 3-Point Arc 
tool is used to draw an arc by
specifying three points: the start point, a through point, and the end point.
The arc passes through all three points.
Using the mouse
The first click sets the start point of the arc.
The second click sets a point the arc passes through.
The third click sets the end point of the arc.
If the points are nearly collinear or identical, a straight line is drawn instead of an arc.
Using the keyboard
Type in the Start Point, the Through Point (as a vector from the start point), and the End Point (also as a vector from the start point) into the input boxes, and press Enter to draw the arc.
| If any two points are the same or nearly collinear, the command falls back to drawing a line. |