Menu: Draw / Ellipse / Ellipse Fixed Ratio 
Creates an ellipse by specifying its aspect ratio - the ratio of the major axis to the minor axis. The axes of the ellipse are orthogonal.
- Enter the aspect ratio in the a:b ratio field on the Inspector Bar. (Lock this value if you want to repeat it later, otherwise the field reverts back to the default.)
- Select the centerpoint of the ellipse.
- Move the mouse to size the ellipse.
Tip: The fixed ratio for an "IsoCircle" (an isometric circle on a cube) is 1.73 (the square root of 3).