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Comment by bri3d | Hacker News Reader

This isn't just a "before quartz oscillators" thing; it's still in extremely widespread use today since quartz oscillators still cost some fraction more than $0. And, it's not always mechanical, there are a lot of all-in-one timekeeping/clock chips that use AC as the reference frequency for their internal oscillator/PLL.

Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference.

Due to the growing complexity of power grids and in Europe, international power-grid politics and infighting, the grid frequency is becoming less stable and you see these devices fluctuate badly more often than they used to. https://hackaday.com/2018/03/09/europe-loses-six-minutes-due...

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> Almost all cheap / "simple" consumer mains appliances, including non-"smart" microwaves, ovens, alarm clocks, etc. still use mains frequency as their time reference.

I find this incredibly hard to believe. Crystals are incredibly cheap and waaaaaay more accurate than anything that the grid does.

If you're not an actual motor, sensing the grid is both an engineering challenge and a non-trivial expense.

To my understanding, the grid is managed to have a fixed number of cycles per day, which would make it perfectly accurate. A cheap crystal can easily lose a few seconds per day. And given how hard it is to keep 60 Hz noise out of circuits, I can’t imagine the sensing would be difficult.

It might be technically possible but it isn't the case any more

Definitely not true in Australia at least, grid frequency can vary by quite a lot from 49Hz to 51Hz.

Does it average out to 60.0000hz over a day/week/month though? It could go that and still have lots of fluctuations.

Certainly not 60.0000 Hz, that is a USA thing. Most of the rest of the world runs on 50 Hz.

The trick is that so many devices use DC power bricks now, because it outsources the UL-or-whatever compliance, and makes FCC easier too. It's much harder to sense 60Hz downstream of that.

Sounds like we need another addition to the USB standard! 60 Hz mode (or 50 Hz, depending on market)

Crystals have very poor long-term performance, though. They can easily be off by several minutes a month, with performance getting worse as they age.

The grid has poor short-term performance, but the long-term frequency is averaged out to be exactly 50/60Hz.

The grid is managed to an exact _average_ frequency. In this way, it essentially acts as a very slow transfer standard for GPS. I own a clock with a 60Hz motor, and while it can vary by anywhere from 5 to 30 seconds throughout a day, this error never accumulates and it recovers back towards zero after any excursions within a day or two.

I have one of those little “binary clocks” (it technically displays in BCD, but it’s still “binary”, right?). When I first set it up, it was running really fast —- like it was gaining hours over the course of a day.

Turns out it had a button combo for “switch between 50Hz and 60Hz mode” that was similar to its combo for (what I thought I was setting) “switch between 12- and 24-hour mode”. (I think the 12/24 switch was “hold the hour button down while plugging in” and the 50/60 switch was “hold both buttons down while plugging in”.)

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