I have a much better appreciation for the volvelles, or circular computers, that survived from the Renaissance and the Enlightenment to the present day.  Fragile, finicky and prone to moving right went you don’t want it to, the volvelle is the brainchild of Raymond Llull, a Catalan Catholic theologian of the mid-1300s AD. 

I want to make a volvelle to go on the inside front cover of a hand bound book I’m designing. As you can probably tell, this volvelle is astronomical in nature, but Llull’s was intended to be logical and grammatical, designed to explore theological concepts and train missionaries to work in Islamic regions (he failed to win many converts).  

The volvelle remains. This one has pointers for the seven visible planets of medieval astronomy (less the Moon, because I lost the paper cutout between cutting it out and assembling the volvelle). It also has a horizon line, and a “sphere of fixed stars” that includes both the Decans of the Zodiac and the Mansions of the Moon; as well as the fixed ground of the twelve houses of astrology. 

And it doesn’t work as smoothly as I’d like. I need to replace the brass brad with a paper system, as is used in medieval and renaissance volvelles. The brass brad is too thick, and doesn’t allow for smooth or independent rotation of the parts. Back to the drawing board.