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Comment by atypeoferror | Hacker News Reader

I recently bought my first not-super-cheap watch, and found out that all around the world there radio stations which broadcast the atomic clock time that a lot of clocks/watches listen to.

After setting the time zone (I guess this also changes the frequency that it listens on) it starts to sync itself using that signal. It is also solar-charging - so this basically means that I never have to touch it. Although it's an analog watch, because of this sync, it correctly handles DST, the date window (including leap year) - basically I never have to touch it again until it breaks . All without bluetooth or internet connection - pretty cool I think.

Casio Oceanus t200 for anyone that cares.

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In the US, those are radio stations WWVB for clocks and watches, and WWV/WWVH for shortwave.

One thing I think is interesting is that not only are the digital formats these carry synced to an atomic clock, but the radio carrier wave is too. So if you need a very precise 10 MHz signal in the lab, you can hook up a shortwave antenna and a filter, and receive the precisely-on-frequency signal broadcast from WWV.

That “all around the world” leaves significant gaps: https://hagensieker.com/2019/11/17/multiband-6-what-is-it/

I had a weather station with an external antenna that could never sync, even during the night, even placed outside in the "best" side of the house on my neck of the EU.

A solar powered, low battery wristwatch that's never outside in the middle of the night will fare much worse.

It's interesting old school tech that works fine in the places where it does work.

For elsewhere, I guess synching through a phone is more practical. So far it works fine. I just hope it doesn't get deprecated (I do, unfortunately, have a feeling the Casio app will break before the radios stop transmitting).

Syncing directly from a 4G signal would be a lot more practical than VLF or HF time signals, but I haven't found a wall clock that does so.

On the one hand, yes. On the other, my country has just shut down 3G and 2G only stays because it's still used by emergency services. How long will 4G last? Longer than bluetooth and the Casio app?

It'd be nice if something like this could be maintained long term. The US, UK and Germany signals have been working since the ~1960s.

Could be, I don't have much experience with it, but so far it has worked every time without me doing anything special - I can check the status of the last sync attempt, which it does nightly on its own (or I can trigger it). The UX isn't great - all manipulation of the seconds hand, but other than that it has been flawless. This is in Germany - your mileage may clearly vary.

As I wrote: it does work great where it does work. I'd definitely have gone that route if it worked where I live. It's just that the marketing that it works "all around the world" falls pretty short, IMO.

I kinda wish the German transmitter had more range (like the US one does) but even the blog I linked to, you can see someone in the continental US who needs to hang their watch from their window blinds for syncing to work reliably.

I even looked into hacking my own transmitter (https://github.com/hzeller/txtempus) before giving up and just buying one of the models with bluetooth phone sync.

I'm pretty sure it's a lot more reasonable to use a fixed set of frequences and use the timezone for offset

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