[peteey]

Crystal errors tend to be around 20 ppm (parts per million)

After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60 *60 = 12 seconds.

Your motherboard probably has a cr2032 keeping it powered when unplugged.

Crystals: https://www.digikey.com/en/products/filter/crystals/171?s=N4...

[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?

[crote]

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!

[moffkalast]

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.

[brohee]

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).

More at https://wwwhome.ewi.utwente.nl/~ptdeboer/misc/mains.html

[throw0101a]

> After a week, 20 ppm would drift 12 * 10^-6 * 7 * 24 * 60 *60 = 12 seconds.

Where are you getting that 12 from?

[dmoy]

It should read 20*, not 12.

The end result is 12 seconds.