Menu: Draw / Circle / Tangent to Arc or Curve 
Creates a circle tangent to an arc, circle, or ellipse.
- Select the existing arc, circle, or ellipse to which you want the circle to be tangent.
- Select the centerpoint of the circle, or enter the radius, diameter, or circumference in the Inspector Bar. (If you use the Inspector Bar and then press Enter, you will not be able to reposition the circle.)
The circle will be created from the point you selected on the tangent object. 
- Move the mouse to position the circle, either inside or outside the tangent object.
