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.
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 :)
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.
It kinda makes you wonder why desktop computers don't use the AC frequency as a stable-ish time source. Short-term accuracy is pretty poor, but it can definitely do better than 12 seconds over a week!
I suppose it's because no AC ever gets to the motherboard in your typical ATX setup? It's all just DC 12/5/3 volts and could be coming from a battery for all it knows. There would need to be an optional standard way of getting time from the PSU and have the AC time keeping there.
Of course, but there's no reason why a 50/60Hz signal couldn't have been included in the ATX power connector back when it was established a few decades ago.
In an alternate universe it would've been put in there, together with all the weird -12V / -5V rails nobody uses these days. Getting it these days would indeed be pretty much impossible.
That's a very optimistic assumption, the target is 50Hz but if it is below or over for a long period of time (e.g. high load in winter making it hard to sustain the nominal frequency) there are no provision to make it run faster or slower unless the time drifted by more than 30s (that's possibly only valid for Europe).
The standards are tighter in the US, with corrections being triggered by 10/3/2s differences and stopping at 6/0.5/0.5s (Eastern/Texas/Western interconnections). Src: https://www.naesb.org/pdf2/weq_bklet_011505_tec_mc.pdf
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.