Just a comment: in a two stage reduction as was proposed, the center pulley must be a compound pulley or gear with two single components fixed side by side on a common shaft or hub. If these two components are exactly the same size, then they are considered to only be an idler and have no effect on the ratio, as Bruno alluded to, although perhaps implying that there was a 'special rule', but that is the basis for it.
If you have a 3 (or more) gear train with a 10 driving a 20 driving a 30, the center component(s) are still idlers and have no effect on the ratio, they are merely motion transmitters.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)