Three inventions moved clocks and watches away from being mechanical/analogue so they could become digital: The quartz crystal, the circuit board and the liquid crystal display.
If you’ve ever wired something—like a lamp—you’ll remember getting out the needle-nose pliers and wire-cutters, maybe a razor blade to strip the insulation off the wire ends; you wrap the exposed copper wire around the appropriate screws then tighten ‘em up so the wire stays put…I’m trying to imagine how you would wire something as minuscule as the insides of a watch. Wires would need to go from the battery to the quartz crystal, back to the battery with a detour to power the hour, minute & second hands after counting how many oscillations the crystal made.
The circuit board is a flat card made of plastic or resin. Instead of wires, circuitry is printed right onto the card in metal ink. A circuit board can get a complicated electric network crammed onto a very small area. A small circuit board in a watch can direct electric power from a battery to the quartz crystal and anything else inside the watch .
You can see the circuit board at 27:20 https://www.youtube.com/watch?v=SFiq8WDx5Is
Those old discarded mass-produced watches and circuit boards can become playthings for someone with electrical knowledge—http://www.angelfire.com/ut/horology/quartz.html
Back to the beginning of The Western Civ User’s Guide to Time & Space