Your understanding isn't incorrect but you're probably expecting smaller time and error scales then there are in practice: Here are some charts of grid time of

Your understanding isn't incorrect but you're probably expecting smaller time and error scales then there are in practice: Here are some charts of grid time offset from 2014 (I think from Menlo Park): http://users.megapathdsl.net/~hmurray/time-nuts/line/Calif-60Hz-2014-2015.png http://users.megapathdsl.net/~hmurray/time-nuts/line/Calif-6... -- so you can see this spanning 60 seconds in a year. [Source post: https://www.febo.com/pipermail/time-nuts/2015-July/092791.html https://www.febo.com/pipermail/time-nuts/2015-July/092791.ht... ] Here is some more recent data: http://users.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-2019.png http://users.megapathdsl.net/~hmurray/time-nuts/60Hz/60Hz-20...