...
- Enter the aspect ratio in the a:b ratio field on the Inspector Bar. (If you want to repeat this value later then lock it, otherwise the field reverts back to the default.)
- Select the centerpoint of the ellipse.
- Move the mouse to size the ellipse.
a:b = 0.5 
a:b = 2.0
...
4. A dotted line appears from the centerpoint. Move the cursor to set the arc start angle, or enter the angle in the Inspector Bar.
5. Move the cursor counterclockwise to draw the arc, or enter the end angle or arc length in the Inspector Bar.
