time@patoka.org said: > For very long time, may be Main Frequency (60 Hz) could be utilised. Say, > MCU could count and compare Zero-Crossings and impulses from DS32xx chips. > After several days, you'll see where it goes. Power in Silicon Valley isn't stable enough to make that approach interesting. Here is the long range view: http://users.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2014-2015.pn g http://users.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2015-Jul.png If you average over long enough to smooth out the daily wobbles, you run the risks of hitting one of their big shifts. 25 seconds over 3 days is almost 100 PPM. -- These are my opinions. I hate spam.