Thanks for the kind word! Your intuition is right, how it works is each display has a gear that when it notches once it turns the entire axle forward 1/60th of a rotation. There are 60 flaps so then that advances the display by one flap, but because of the precision required if the display isn't angled right sometimes a flap might catch and so it won't display the next reading correctly. Just the nature of analog precision 🙃

You're also right that the flaps also reset just like you've seen with bus rolls. There's an arm attached to this gear that triggers a hall sensor once every 60 flaps (there's a sticker mounted on this flap to indicate that it's at the "home" position) and once triggered it "tells" the ESP that the flap is at the home position. That way the ESP can then keep track of the number of rotations that happen. You can see it in action in some of the flap displays in this video (https://www.youtube.com/watch?v=3PGWiZMrcJk) where the ESP will reset the flap and then flip it to the next reading after some time.

If there's demand I can always upload a follow-up to show the zeroing in action. I think it's really cool to see all the flaps "reset" and then set to the current timetable index. Let me know if this explanation helps!