Thank you thomthom, that is exactly what I was looking for.

http://www.sketchup.com/intl/en/developer/docs/ourdoc/ui#set_cursor http://www.sketchup.com/intl/en/developer/docs/ourdoc/tool#onSetCursor

I could change it so it recalculates the end_angle as well, that way I would not have to worry what SketchUp says the angle is. But I think I have bigger issues than that.

find_faces was exactly what I was looking for. Thanks,

I agree, if you post here, most beginners won't have any clue about ruby. Post in the ruby discussion group and there are lots of us there who can help. Chris

Excellent. There's already a script out there that does this, but it does not work very well for me. Specifically, it often selects a vertex behind the one I want, and then gives an incorrect angle. It would be much better if you could restrict it to act only in a given plane, like the native protractor tool. The existing script by Didier Bur is called dim_angle.rb, and can be found here: http://www.crai.archi.fr/RubyLibraryDepot/Ruby/em_arc_page.htm

I'm getting closer. It turns out that ArcCurve.start_angle is always 0.0, so I made a function that finds the actual start anlge, I then add that to the end angle for output. def get_new_angle(center, point) #center is the center point returned by AcrCurve.center #point is the start point of the arc returned by ArcCurve.vertices[0].position return Math;;atan(((center.y.to_f - point.y.to_f)/(center.x.to_f - point.x.to_f))).to_f.degrees.abs end Now the problem is arcs on the y axis are not correct.