It’s a diagram of an old clock where the numbers flip down. Also, a gnome lives inside.
Sometimes you know a person long enough that something they said in passing way back when bubbles back up. Such is the case with the clock pictured here in the diagram.
About the time I knew I wanted to make a clock where the numbers flip down I came across a tutorial for making exploded-view isometric diagrams. This birthday poster series has been an opportunity to try different things artistically and I felt in this case that the subject (the clock) and its presentation (as a diagram) would be appreciated by the recipient.
Thematically, I decided from there that I wanted a clock that was operated by the gnome living inside.