It even works in Silverlight

Go on - click anywhere in between the 2 arcs (representing the arm’s addressable area).

[simply-silverlight xap=tintoy/SilverArm.xap width=500 height=500 float=none]

If I have time, next week, I’ll have a go at animating it (I have some ideas for doing the acceleration without resorting to using Silverlight animation, which wouldn’t be as much fun).