I like to build a device that needs long term time stability. In germany, one of the best simple clocks use the mains power frequency to obtain a time measure. While the frequency is allowed to change a little with the power net load, the errors are nullified over longer periods, usually over night. So in the long term, a mains driven clock is actually atomic clock driven and very precise.
This applies to the whole european power network I guess.
So I wonder how about other countrys worldwide? Would it be feasable to use mains frequency for timing issues after adjusting to a country's official frequency?