I'm in the middle of a repair that calls for new legs, and they need to be identical, which means pattern work. But there are some compound angles and curves involved, so tracing patterns requires some trickery.
I won't go too far into the logistics, but having one of these helps. Basically, it's a straight edge that comes up at 90 degrees to the surface that it rides on, and at the bottom of the edge is a mechanical pencil. So, regardless of where the object is, above the plane that the pattern is traced onto, the projected profile will be accurately traced.
And yes, that's a Miller dowel being used to push the button on the pencil. Miller dowels! Oh, the shame!