Thanks Russell. I'll incorporate some of those changes.
I think we have to define position and orientation.

Perhaps, but I'd like to believe that pilots & airplane builders can
understand that their propellers rotate but do not change position.
Rotate is a change in rho or theta(*), while position is a change in x,
y, or z.

I never had a Spirograph.

Ah. I think I've discovered your next Christmas gift... (What's your
postal address again?)
For your further reading pleasure:
http://en.wikipedia.org/wiki/Spirograph

Maybe both planetary and first phase roulette.

First phase Roulette isn't helpful: the ball and wheel are in
counter-rotation.

Russell Kent

(*) Actually, I think there's a third rotational dimension in there, but
I can't recall the Greek letter traditionally used to denote it.



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