[fanf2]

There’s a fun thing about quartz wristwatches: one of the biggest contributions to frequency fluctuations in a quartz oscillator is temperature. But if it is strapped to your wrist, it is coupled to your body’s temperature homeostasis. So a quartz watch can easily be more accurate than a quartz clock!

Really good watches allow you to adjust their rate, so if it runs slightly fast or slow at your wrist temperature, you can correct it.

One of the key insights of John Harrison, who won the Longitude prize, was that it doesn’t matter so much if a clock runs slightly fast or slightly slow, so long as it ticks at a very steady rate. Then you can characterise its frequency offset, and use that as a correction factor to get the correct GMT after weeks at sea.

[lxgr]

That would require tuning it to the average body temperature though, right?

Or are you saying that what makes quartz crystals drift is the change in temperature?

[fanf2]

Both are true :-)

[lxgr]

Oh, I missed your comment about being able to tune some wristwatches quartz! I wasn't aware that was a thing.

Still, wouldn't the temperature of a watch while being worn vary as least as much as when sitting in a drawer (unless you live in a region blessed with t-shirt weather year around)?

One of my favorite wristwatches I used to wear as a teenager had a thermometer, but I don't remember how exactly that varied over the year, just that it always showed neither quite my body temperature, nor quite the ambient one :)

[labcomputer]

The crystals used in watches are usually cut and selected so that a local minimum or local maximum of the tempco is near the temperature of your wrist.

Thus, the tempco is near zero, so human-to-human differences don’t matter much.

One thing to notice is that quartz watches almost always have a metal backplate touching your wrist so that the crystal can have good thermal contact. Presumably, the thermometer in your watch was decoupled from that plate.