As an aid to carving round spinners (and other airplane parts), I cut a drafting circle template into strips. I can put the appropriate diameter hole right over the carved piece to see how close or far out of round it is. It is also useful to have jewelers files or emery boards for shaping.
Thanks for sharing, Dave. I think I might have something like that stashed in a drawer somewhere.
Better than my Eyeball Computer.
Louis