If my computer wouldn’t synchronize with a NTP server, how precise would its clock be? How much would its clock/time deviate, especially compared to a quartz or mechanical watch?
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.
Because network-synchronized time clients are now nearly everywhere, the cost and accuracy of onboard computer clocks has declined over the past decade.<p>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.<p>> How much would its clock/time deviate, especially compared to a quartz or mechanical watch?<p>In my experience, quite a lot. To see this for yourself, log two machines onto <a href="http://arachnoid.com/NaturalResources/big_clock.html" rel="nofollow">http://arachnoid.com/NaturalResources/big_clock.html</a>. On one machine, make a local copy of the page and disconnect from the Internet. See how quickly that machine deviates from correct time.