Digital watches have been around for a while now, first released to the public by Pulsar in 1972. I thought recently how much we take it for granted how they just work so accurately, and that's aside from all the extra fancy features you can get, like stopwatches, countdown timers, and alarms. Are they a small computer?
They aren't quite clever enough to be considered a computer of any sort. They don’t have the same ticking mechanism like a watch with a dial and hands, they use a tiny piece of quartz crystal.
An electrical charge is sent from the battery to the quartz crystal, which then acts as an oscillator (going back and forth), vibrating at precisely 32,768 times per second - this in itself sounds like a topic for another post! The display of a digital watch is controlled by a piece of the circuit called the counter. This counts the pulses coming from the oscillating quartz crystal and then makes the display of a digital watch progress by one second. The watch’s microchip then converts this into hours, minutes and seconds.
Even though this almost magical crystal keeps very accurate time, it does not stay perfectly accurate forever and therefore you occasionally need to adjust your watch's time. Batteries will last for years but as they loose power the oscillator can slightly slow, and cause inaccurate time.