Comment 7 for bug 692719

Ok, here is the next try (patch generated with bzr diff of trunk).

I changed the inner circle into a sodipodi arc. This allows one to use the circle tool to change the radius. There is definitely a trade-off here - editing with the circle tool allows the user to easily adjust the radius, but for someone who is creating the gear to animate it might not be as good due to the center not being explicit in the SVG element.

In terms of percentage vs. absolute measure, for me at least the absolute measure is more useful, as it allows me to size the center hub to the right size for a shaft when cutting out using a laser cutter. With this in mind I also added an option to specify the sizes (both pitch and center hole) in different units (px, in, and mm), and also changed the measure to be the diameter, rather than the radius (since if you are sizing it to fit a shaft, you typically are thinking of the diameter of the shaft, rather than the radius).