I'd say you are spot on, with no way to adjust the centerline spacing on the 2 shafts, some very interesting tooth designs come into play, there are also "combo gears" that with one large gear, and 2 smaller gears, but with a different tooth count, but cut so they mesh, you can have 2 ratio's, and only 3 gears, the smaller gear for instance, will be some times be marked 13/14 or something like that, and it will mesh correctly with a larger one, giving 2 ratios. Bob