And in hours, minutes and seconds. Yes, those are near universal (I guess there may still be a few tribes in the Amazon or Indonesia that don’t use them), but still are cultural.

Also, having each hour have the same duration is cultural. The Romans, for example, at some time, used a clock where “the period of the natural day from sunrise to sunset was divided into twelve hours” (https://en.wikipedia.org/wiki/Roman_timekeeping). That means hours were shorter in winter than in summer.

I was also confused why the outer ring must only show zero or one, and then it struck me — twelve hour system.