[ThisNameIsTaken]

Not sure it's precise enough though. In 2018, many clocks in Europe were off because the frequency on the net had drifted due to (as I understood it) the network being out of sync across various countries. Some here might actually understand the details of this.

[mystified5016]

In the US, we modulate (or used to) grid frequency specifically for these analog clocks such that in a 24hr period it averages to exactly 60Hz.

It doesn't really matter on a second-to-second timescale how accurate grid frequency is. If you can keep the average frequency right, all your clocks will speed up and slow down in sync, and average out to 24hours per day

[wongarsu]

The frequency drifts up and down whenever demand doesn't exactly match supply. Higher demand slows the frequency down, higher supply speeds it up. This is actually the main way power companies know if supply and demand match, and if power stations have to ramp up or down.

The frequency changes are pretty small in normal operation, but on a clock that uses the frequency to keep time they accumulate. They only work reliably because power companies know about them and occasionally deliberately run a bit over or under capacity to make the average match again.

[andlier]

Fun fact, there are databases of the exact frequency vs. time and it can be used to accurately time stamp audio/video recordings by correlating the ~50/60hz noise in the recording with the database. Good writeup on the technique and how it has been used in court cases: https://robertheaton.com/enf/

[kps]

In 2018 the European grid lost a cumulative 6 minutes due to a Serbia/Kosovo dispute.

[folli]

This is fascinating, didn't know. Why does higher demand lower the frequency?

[nottorp]

I don't think 60 or 50 Hz matters wrt to this.

The only thing that matters is that a clock that expects a certain frequency gets that frequency and not 1% more or 1% less.