[agoetz]

Most RTCs do use the same crystals that are in wristwatches, which is actually the source of their error.

The tuning fork crystal design used in wrist watches has a parabolic temperature coefficient, which means that the clock is only really accurate at room temperature. This isn't a problem for wristwatches, because, presumably your wrist is at approximately room temperature, but it does become a problem for electronics that operate with large temperature swings. (like the inside of a phone or computer, for instance).

https://www.maximintegrated.com/en/app-notes/index.mvp/id/58

[Florin_Andrei]

The vast majority of quartz references in consumer devices could be a lot better, but they are not fine-tuned at the factory. They're just "close enough". So they drift a lot.

A simple tuning procedure could make almost all quartz clocks you own a heck of a lot better. But in many cases this is hard to do because the manufacturer never put the tuning components (a variable capacitor or the like) on the PCB.

[monochromatic]

That’s interesting. I’d never thought about it, but of course there’s a temperature dependence, and of course attaching it to a wrist mitigates it.