# What causes clock drift in quartz oscillators?

Usually, computer seem to use quartz oscillators. In contrast to atomic caesium clocks they seem to have a relatively big drift and thus we need protocols like NTP to correct them.

What causes this clock drift in quartz oscillators? Is it something that could be improved? Are there some fundamental properties stopping quartz oscillators from reaching some accuracy? And what is this accuracy?

• Engineering answer: if you have NTP available, there's no point making the on-board clock more accurate, especially if it requires increasing the cost. – The Photon Sep 30 '18 at 16:34
• @ThePhoton What would you say would be the most extreme inaccuracy that is sill acceptable be? A possible answer I can think of: NTP stops working once the internal clock is more than 1000s off. As NTP cannot be active when the computer is shut down, a clock drift by more than 1000s over 3 weeks (a longer vaccation) seems unacceptable. So the clock drift should be less than 47s a day. But besides that, I would not be sure if other things still work correctly if the clock drift was that heavy. – Martin Thoma Sep 30 '18 at 16:48

...the oven-controlled crystal oscillator (OCXO) achieves the best frequency stability possible from a crystal. The short term frequency stability of OCXOs is typically $$1 \times 10^{−12}$$ over a few seconds, while the long term stability is limited to around $$1 \times 10^{−8}$$ (10 ppb) per year by aging of the crystal.1 Achieving better performance requires switching to an atomic frequency standard, such as a rubidium standard, caesium standard, or hydrogen maser. Another cheaper alternative is to discipline a crystal oscillator with a GPS time signal, creating a GPS-disciplined oscillator (GPSDO). Using a GPS receiver that can generate accurate time signals (down to within ~30 ns of UTC), a GPSDO can maintain oscillation accuracy of $$10^{−13}$$ for extended periods of time. (Wikipedia: Crystal Oven)