Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?
As I was studying electronics at the time I brought the watch to the lab and opened it and connected a frequency counter to the oscillator, you could clearly see the crystal and a little trimming pot (I don't remember by now if that was a pot or something else - capacitor maybe), and adjusted it to exactly 32768Hz.
After that the watch drifted less than one second per month, and it kept the stability for the rest of the year (until a bicycle accident which resulted in a smashed watch).
I've never since owned a watch which was even close to that. They're drifting so much that I can't even rely on my watch to catch the bus (there's a stop outside my home and the bus is there exactly on time).
So that would locate you pretty unambiguously in Switzerland then?
This was the vibe I got when the first pre-always-on Apple Watches were first introduced with Raise to Wake - where you had to actively do an action to see the time.
The watch uses the WWVB signal for nightly syncing. However, living on the East Coast means syncing is very dependent on day-to-day atmospheric propagation. When I visit more inland, it works great.
The watch face is solar powered, so I’ve never had to change the battery.
It has since been retired after 8 years of use for an Apple Watch, but I think fondly of the mighty job it did.
Actually in the process of choosing a casio lineage (waveceptor movement, metal case, sapphire crystal) - do I get titanium or blacked out stainless steel, lol
My synced G-Shock is always correct to within better than one tenth of a second, that is, to the limit of observability. Solar powered, too, so it's just an utterly reliable black box. My favourite gadget by far.
NTP isn't nearly that inaccurate.
What's winter like in Japan? Is it freezing?
Actually one of the earliest quartz watches on the market from Omega used a 2MHz crystal and was very accurate. Personally I own a Seiko with a 200kHz system, which is good for about 20s/year. Then there are the thermo stabilized systems, which are even more accuarate. The problem is, that the frequency of the crystal depends on its temperature which is the main source of time inaccuracy (there are some watch enthusiasts which do get egg breeding cupboards which have constant temperatures up to tenths of degrees, they make for very accurate watches).
Currently, the best movements on the market are accurate to about 5s/year, which is pretty amazing considering the watches are worn on your wrist in varying conditions. With my precise Seiko watch I could even notice a slight change in speed when I moved quite a distance to a different town with slightly different weather. That shows how big a challenge a really accuarate wrist watch is.
Then there are the market concerns. The most basic and cheap quartz are already accurate enough for most non-enthusiasts. Then, after almost being killed by quartz watches in the 80ies, the luxury watch industry managed to establish a mechanical movement as the desirable item. So there are few expensive quartz watches left on the market, which would feature more sophisticated movements with higher accuracy. And finally, there is a range of higher value watches which receives time signals, be it official time signals in several regions or just GPS signals.
Cornered like this in the market, unfortunately not much money went into high-precisions movements. There are still a few on the market from Seiko, Breitling, Omega and Citizen (there might be more, but those come to my mind). And of course there is the Apple Watch, which is rather affordable and just uses NTP to get absolute precise timing.
Assuming you wear the watch.
15 seconds per month is about 6 parts per million, which is already better than the manufacturing tolerances of a typical cheap quartz crystal. There are very few objects of any kind that you can obtain cheaply with that kind of accuracy. That suggests that, as this article says, Casio is trimming the frequency for each watch to compensate for component variations.
I have to admit, for my day to day use I am happy if I am less than five minutes off.
Seiko 5 automatics have been reported to lose 30 seconds a month, even as little as 12 seconds a month.
I mean, we have accurate electric timepieces now, and the F91-W came out in 1989; we had accurate electric timepieces then, too.
it's a cost versus value thing.
This is 34 years old technology. You can get GPS watches relatively cheap and they'd sync with satellites automatically and always remain accurate.
Of course, with any HackRF you can also generate GPS signals.
But it would be a lot less necessary if the watches had reasonable temperature compensation. Obviously the crystal frequency shifts with temperature, and they're typically adjusted to achieve best accuracy when at "wrist temperature" for 16 hours a day, and "nightstand temperature" for 8. Any deviation from that, routine, and crystal accuracy gets terrible.
Temperature-compensated crystal oscillators (TCXOs) switch tiny capacitors in and out of (or bias a varicap in) the crystal loading circuit to "rockbend" its response and keep it nearly flat across a wider range of temperature, but this requires extra power. A minuscule amount, but it adds up quickly when your budget is nanowatts.
However, there's another way to do it, which I'm astonished not to see: You don't need to alter the crystal's actual frequency if you can just adjust the number of counts that represent a second. Every once in a while (every few minutes would be plenty), take a temperature reading, look it up in your calibration table, and stuff or steal a few cycles from the counter register.
This takes basically no additional power, adds one more calibration step at the factory, and should bring drift down by an order of magnitude, into TCXO territory. Seconds per year, not seconds per month. That would be something to crow about, and it baffles me that Casio and others never went that route.
Verilog came out in 1984, but its use for synthesis (i.e. actually compiling text into circuits) was not popularized until much later, after correctness bugs in synthesizers and various other advancements in design tooling came around. It might have been used as a simulation/verification language for the digital portions of this chip.
The two languages fill the same role in the ecosystem, I have to say that I have never used ether, but my impression is that vhdl has clearer syntax(if you can stomach it's ada look and feel) and verilog has better tooling. which makes sense considering that one was a documentation project and the other was an internal tool for simulation that escaped into the wild.
There are other high-accuracy watches (it's mostly a Japanese market thing), and I believe +/- 10 seconds a year is considered fairly pedestrian in that world.
The F-91W might not actually have anything resembling software; just fixed function mixed-signal circuitry, but I haven't investigated it. Given the timing of its release, it's possible that an HDL was used, but also possible it was designed at the circuit level with CAD. The F-87W (which the 91W replaced) predates either VHDL or Verilog.
Seiko 5 automatics apparently[1] can.[2]
[1] https://www.watchuseek.com/threads/seiko-5-is-pretty-accurat...
After observing Seiko 5 SNK809 for 35 days, I can say I´m happy with accuracy.
Overall, it has lost 25 seconds during this time.
It lost most of it when it was sitting on table 2 times during observation. When kept on wrist, it hardly lost any...