There were pebbles with displays? Crazy. Finding a good dot matrix display takes me longer than a half hour - I don't need 5000, nor do I want to pay $40 each.

There were pebbles with displays? Crazy. Finding a good dot matrix display takes me longer than a half hour - I don't need 5000, nor do I want to pay $40 each. E-ink needs to be cheaper, I think it's probably good enough for stuff like watches. There are arduinos with breadboards that are between US dime and US quarter sized, if I wanted the exact feature set I'd probably start there. Seeed or sparkfun or adafruit sells the little demo boards. Solder on a tiny lithium battery and charging/buck circuit, and a 9dof spatial sensor, and a prototype is born. If you could get a metal clamshell around it and a band, you could have a watch that's overall smaller than the apple watches of yore.