
Ask HN: How precise are computer clocks? - N0RMAN
If my computer wouldn’t synchronize with a NTP server, how precise would its clock be? How much would its clock&#x2F;time deviate, especially compared to a quartz or mechanical watch?
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anonymous_iam
Generally the RTC in a computer is not as accurate as a typical wall clock or
wristwatch. Although the RTC usually uses the same type of crystal as a watch,
the circuit is not usually calibrated (tuned) as part of the production and
test process. I have seen drift rates of up to 5-10 minutes per month on
systems that aren't using NTP.

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lutusp
Because network-synchronized time clients are now nearly everywhere, the cost
and accuracy of onboard computer clocks has declined over the past decade.

At the extreme, Raspberry Pis don't even have an integrated battery-sustained
clock, and if the Pi has no network connection, it has no time at all.

> How much would its clock/time deviate, especially compared to a quartz or
> mechanical watch?

In my experience, quite a lot. To see this for yourself, log two machines onto
[http://arachnoid.com/NaturalResources/big_clock.html](http://arachnoid.com/NaturalResources/big_clock.html).
On one machine, make a local copy of the page and disconnect from the
Internet. See how quickly that machine deviates from correct time.

