The mechanism needs to be beautiful and symmetric, with consistent curves and thicknesses making everything appear to be “cut from the same cloth”. This begins with lots and lots of sketches.
This is all very rough, but I think it’s headed the right direction. The gears for months and days of the month are the same distance from the center, and the same diameter. The pivot points of the two main levers and the detent levers form a perfect rectangle. The springs for these levers are nice and symmetric, etc. Lots of additional sketches (and computations) will be needed to refine all this. It’ll soon make sense to move the design work into CAD.
Making A Perpetual Calendar Watch 