The build relies on that old stalwart, the Arduino Uno, to run the show. It’s hooked up to a DS3231 real-time clock module so it can keep accurate time for long periods, as is befitting a clock.

When you read “Arduino wristwatch”, you fall into ... One IC is an AVR micro, of course. The other is a DS3231 real time clock with built-in crystal. A CR2032 keeps it all running.