Hi Morten, just one more note - the kind of spiral that MoI is producing is this one here:

http://en.wikipedia.org/wiki/Archimedean_spiral

The end tangents on that kind of spiral are not supposed to coincide with tangents of the outer radius or inner radius circles, a spiral like this is a "whole different kettle of fish" from just a circle because of its continuously changing nature.

- Michael