7 ms·

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal

by vasqw 4y ago

I bought one of those recently and I was surprised by how inaccurate it was. It drifted like 15 seconds every month. From what I've been reading, that is normal, but I was surprised - with all the technological advances that we have it is odd to think that cheap timekeeping is not a solved problem yet! Also: how is the software of these watches without a CPU designed? Is it something like Verilog or whatever?

serf 4y ago
>yet 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.
teraflop 4y ago
It's easy to make a digital circuit that counts clock cycles with perfect accuracy. But for any clock, the actual length of each cycle is dependent on analog processes, and it's impossible to completely eliminate errors. 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.
faisalhackshah 4y ago
15 seconds per month is about 6.7ppm. That's well within typical crystal oscillator accuracy. If you need more than that (without external time correction such as gps or radio/internet), you need expensive oscillators with temperature compensation or even ovenized units.
sn_master 4y ago
> all the technological advances that we have This is 34 years old technology. You can get GPS watches relatively cheap and they'd sync with satellites automatically and always remain accurate.
- vasqw 4y ago
  Yes. I ended up buying a GWM5610 which synchronises through radio. It's cool. But still I would have hoped there would be a better "local" (i.e. self-reliant) solution.
  - myself248 4y ago
    There's software for the Beaglebone PRU so you can generate your own WWV signal, for receivers buried too deep into buildings or otherwise suffering from poor signal. 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.
    - erosenbe0 4y ago
      Nxp sells a PCF2131 with an internal TCXO that runs on 64 nanoamps when not doing anything else. So with a modern CMOS process, the TCXO itself is not a big deal. A clock pin at 32768 cyc/s looks to be way more power hungry, which tells us that an ideal low-power solution is an all-in-one SoC.
  - 4y ago
Tor3 4y ago
At around 1976-1977 I bought one of those fancy new LED wristwatches, where you pressed a button and the time lit up in red. Straight out of James Bond, as I recall. 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).
- dekhn 4y ago
  People who are curious about this, it's worth reading about quartz oscillators in watches and in particular, methods of calibrating them: https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compen...
- smackeyacky 4y ago
  Get a Casio G-Shock. The 800 models can sync with your phone and the time is auto corrected. I bought a GBA-800 from a pawn broker - out of the dozen or so watches in my box it's the one I reach for if I have to know what time it is accurately.
  - xattt 4y ago
    One of my best bang-for-the-buck purchases was a Casio Waveceptor watch with a hybrid clock face. 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.
    - 4y ago
_ph_ 4y ago
Almost all quartz watches have a similiar movement, running of a 32kHz crystal. Those give you about 15s/month accuracy, which is an oder of magnitude better than most mechanical watches and that for a very few bucks. More precise quartz watches exists, but they require quite a bit more effort, which of course translates into costs. 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.
- klodolph 4y ago
  To add to this—I’d say that watches are quasi-temperature-controlled. You wear the watch in varying conditions, but most people spend most of their time in controlled environments, and the watch is directly next to your body, which itself is temperature-regulated. This just means that temperature drift may be less of a factor for watches than it might be for, say, a clock on the wall or in a car. Assuming you wear the watch.
hotpotamus 4y ago
Citizen has a movement where they throw all the tech they have at it to guarantee 1 second per year accuracy. I remember things like quartz crystals have aging effects, so they used pre-aged crystals - little details like that. It even has an anti backlash mechanism on the second hand so that it ticks perfectly with no visible wobble. It probably doesn't make sense when it would be much cheaper to just use an external radio/GPS time source, but as a watch company, it makes a statement about their craft. 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.
jimmyjazz14 4y ago
Citizen has a quartz movement that is rated to only drift plus or minus 5 seconds a YEAR which is quite impressive though they cost around 2000 dollars and are exclusive to the Japanese market. Several other brands out there make high accuracy quartz movements (which is done with thermal compensation) but they do generally cost more than cheap Casios.
kube-system 4y ago
While 15 seconds per month is within Casio’s spec for this, it’s also worth noting that there’s reportedly a lot of counterfeits of the F-91W floating around. I got one once from a major marketplace.
aidenn0 4y ago
~1s per day is normal for a non-temperature-compensated quartz crystal. The cheap solution is to just sync to LF time transmissions (or GPS if not running on battery power). 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.
somat 4y ago
A fair assessment, but I find it funny that 15 seconds per month is considered inaccurate, analog watches would kill for that sort of accuracy, a railroad quality pocket watch for example must loose no more than 30 seconds per week. I would guess that as smartphones are replacement for the pocketwatch, The way their network connected, never drift clock works becomes the new normal. I have to admit, for my day to day use I am happy if I am less than five minutes off.
- Maursault 4y ago
  > analog watches would kill for that sort of accuracy Seiko 5 automatics have been reported to lose 30 seconds a month, even as little as 12 seconds a month.
- lmz 4y ago
  You mean Mechanical watches, not Analog ones. There are lots of Analog quartz watches with 15s/month accuracy.
leeoniya 4y ago
my automatic Aqua Terra (8800 movement) maintains this (or better) accuracy, which i find astounding for a mechanical gear train that oscillates at 3.5Hz. i definitely would expect a well-tuned quartz movement to outperform this significantly. but i guess not for < $20 :p
gleenn 4y ago
You might be surprised to learn a lot of servers even have largish time drift. I might be repeating info which is getting out of date but I heard 30 second drift isn't uncommon. Obviously doing NTP syncing more frequently would probably help that.
- post-it 4y ago
  Yeah, the React Native debugger is broken on my Pixel because the time is different from my laptop by ~0.5 s, so short taps register as long presses or something like that.
  - Brian_K_White 4y ago
    If it's comparing times from two different devices, then it's not broken because of the difference in times.
    - post-it 4y ago
      If it's broken because the designer assumed any two devices would have a sub-second time difference, it's still broken.
      - Brian_K_White 4y ago
        Yes my point was to say that it's broken.
        post-it 4y ago
        Oh I see, I misunderstood initially but I got it when rereading.
iron2disulfide 4y ago
The functionality of the F-91W is simple enough that I don't think a CPU would even be needed. Probably the digital parts of this chip are just state machines. That being said, the left half of the die shot looks like some kind of gigantic ROM, which could either be used by a CPU (as static program memory) or just transition logic/data for any generic state machine(s). 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.
- somat 4y ago
  vhdl started as a project to document integrated circuits. The department of defense was getting a lot, and more complicated, integrated circuits and wanted a standard to document the functionality. At some point someone thought, "you know, if the documentation is good enough we could reverse it and synthesize a circuit from it", and thus why you use vhdl(or more likely verilog) to program your fpga. 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.
nightowl_games 4y ago
Anecdotal but my F-91W is currently 8s behind my phone, which I sync'd together about 6 months ago. I've always felt very impressed with how accurate it is.
ashwinne 4y ago
I was surprised by this inaccuracy too. But was impressed when I learnt that there is no analog wristwatch that can match this accuracy - they are all far far worse. (Isn't it shocking that all those super-expensive Rolexes and whatnot are all going off by minutes per month!) Get one of the Casio watches that syncs to atomic clock radio signals every night - it will be second-accurate all the time.
- Maursault 4y ago
  > But was impressed when I learnt that there is no analog wristwatch that can match this accuracy Seiko 5 automatics apparently[1] can.[2] [1] https://www.watchuseek.com/threads/seiko-5-is-pretty-accurate.410417/post-5522035 https://www.watchuseek.com/threads/seiko-5-is-pretty-accurat... [2] https://qr.ae/prvf6L https://qr.ae/prvf6L
  - klodolph 4y ago
    According to the linked thread, the Seiko 5 is an order of magnitude worse… 5 seconds per day, versus 15 seconds per month for a quartz watch.
    - Maursault 4y ago
      This one? 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...
chinabot 4y ago
It will be calibrated for room temperature, temperature changes do affect the oscillator frequency that is why highly accurate frequency sources have an "Oven" to keep the temperature stable https://en.wikipedia.org/wiki/Crystal_oven https://en.wikipedia.org/wiki/Crystal_oven

by vasqw 4y ago

serf 4y ago

>yet 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.

teraflop 4y ago

It's easy to make a digital circuit that counts clock cycles with perfect accuracy. But for any clock, the actual length of each cycle is dependent on analog processes, and it's impossible to completely eliminate errors. 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.

faisalhackshah 4y ago

15 seconds per month is about 6.7ppm. That's well within typical crystal oscillator accuracy. If you need more than that (without external time correction such as gps or radio/internet), you need expensive oscillators with temperature compensation or even ovenized units.

sn_master 4y ago

> all the technological advances that we have This is 34 years old technology. You can get GPS watches relatively cheap and they'd sync with satellites automatically and always remain accurate.

vasqw 4y ago
Yes. I ended up buying a GWM5610 which synchronises through radio. It's cool. But still I would have hoped there would be a better "local" (i.e. self-reliant) solution.
- myself248 4y ago
  There's software for the Beaglebone PRU so you can generate your own WWV signal, for receivers buried too deep into buildings or otherwise suffering from poor signal. 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.
  - erosenbe0 4y ago
    Nxp sells a PCF2131 with an internal TCXO that runs on 64 nanoamps when not doing anything else. So with a modern CMOS process, the TCXO itself is not a big deal. A clock pin at 32768 cyc/s looks to be way more power hungry, which tells us that an ideal low-power solution is an all-in-one SoC.
- 4y ago

Tor3 4y ago

At around 1976-1977 I bought one of those fancy new LED wristwatches, where you pressed a button and the time lit up in red. Straight out of James Bond, as I recall. 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).

dekhn 4y ago
People who are curious about this, it's worth reading about quartz oscillators in watches and in particular, methods of calibrating them: https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compensation https://en.wikipedia.org/wiki/Quartz_clock#Inhibition_compen...
smackeyacky 4y ago
Get a Casio G-Shock. The 800 models can sync with your phone and the time is auto corrected. I bought a GBA-800 from a pawn broker - out of the dozen or so watches in my box it's the one I reach for if I have to know what time it is accurately.
- xattt 4y ago
  One of my best bang-for-the-buck purchases was a Casio Waveceptor watch with a hybrid clock face. 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.
  - 4y ago

_ph_ 4y ago

Almost all quartz watches have a similiar movement, running of a 32kHz crystal. Those give you about 15s/month accuracy, which is an oder of magnitude better than most mechanical watches and that for a very few bucks. More precise quartz watches exists, but they require quite a bit more effort, which of course translates into costs. 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.

klodolph 4y ago
To add to this—I’d say that watches are quasi-temperature-controlled. You wear the watch in varying conditions, but most people spend most of their time in controlled environments, and the watch is directly next to your body, which itself is temperature-regulated. This just means that temperature drift may be less of a factor for watches than it might be for, say, a clock on the wall or in a car. Assuming you wear the watch.

hotpotamus 4y ago

Citizen has a movement where they throw all the tech they have at it to guarantee 1 second per year accuracy. I remember things like quartz crystals have aging effects, so they used pre-aged crystals - little details like that. It even has an anti backlash mechanism on the second hand so that it ticks perfectly with no visible wobble. It probably doesn't make sense when it would be much cheaper to just use an external radio/GPS time source, but as a watch company, it makes a statement about their craft. 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.

jimmyjazz14 4y ago

Citizen has a quartz movement that is rated to only drift plus or minus 5 seconds a YEAR which is quite impressive though they cost around 2000 dollars and are exclusive to the Japanese market. Several other brands out there make high accuracy quartz movements (which is done with thermal compensation) but they do generally cost more than cheap Casios.

kube-system 4y ago

While 15 seconds per month is within Casio’s spec for this, it’s also worth noting that there’s reportedly a lot of counterfeits of the F-91W floating around. I got one once from a major marketplace.

aidenn0 4y ago

~1s per day is normal for a non-temperature-compensated quartz crystal. The cheap solution is to just sync to LF time transmissions (or GPS if not running on battery power). 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.

somat 4y ago

A fair assessment, but I find it funny that 15 seconds per month is considered inaccurate, analog watches would kill for that sort of accuracy, a railroad quality pocket watch for example must loose no more than 30 seconds per week. I would guess that as smartphones are replacement for the pocketwatch, The way their network connected, never drift clock works becomes the new normal. I have to admit, for my day to day use I am happy if I am less than five minutes off.

Maursault 4y ago
> analog watches would kill for that sort of accuracy Seiko 5 automatics have been reported to lose 30 seconds a month, even as little as 12 seconds a month.
lmz 4y ago
You mean Mechanical watches, not Analog ones. There are lots of Analog quartz watches with 15s/month accuracy.

leeoniya 4y ago

my automatic Aqua Terra (8800 movement) maintains this (or better) accuracy, which i find astounding for a mechanical gear train that oscillates at 3.5Hz. i definitely would expect a well-tuned quartz movement to outperform this significantly. but i guess not for < $20 :p

gleenn 4y ago

You might be surprised to learn a lot of servers even have largish time drift. I might be repeating info which is getting out of date but I heard 30 second drift isn't uncommon. Obviously doing NTP syncing more frequently would probably help that.

post-it 4y ago
Yeah, the React Native debugger is broken on my Pixel because the time is different from my laptop by ~0.5 s, so short taps register as long presses or something like that.
- Brian_K_White 4y ago
  If it's comparing times from two different devices, then it's not broken because of the difference in times.
  - post-it 4y ago
    If it's broken because the designer assumed any two devices would have a sub-second time difference, it's still broken.
    - Brian_K_White 4y ago
      Yes my point was to say that it's broken.
      - post-it 4y ago
        Oh I see, I misunderstood initially but I got it when rereading.

iron2disulfide 4y ago

The functionality of the F-91W is simple enough that I don't think a CPU would even be needed. Probably the digital parts of this chip are just state machines. That being said, the left half of the die shot looks like some kind of gigantic ROM, which could either be used by a CPU (as static program memory) or just transition logic/data for any generic state machine(s). 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.

somat 4y ago
vhdl started as a project to document integrated circuits. The department of defense was getting a lot, and more complicated, integrated circuits and wanted a standard to document the functionality. At some point someone thought, "you know, if the documentation is good enough we could reverse it and synthesize a circuit from it", and thus why you use vhdl(or more likely verilog) to program your fpga. 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.

nightowl_games 4y ago

Anecdotal but my F-91W is currently 8s behind my phone, which I sync'd together about 6 months ago. I've always felt very impressed with how accurate it is.

ashwinne 4y ago

I was surprised by this inaccuracy too. But was impressed when I learnt that there is no analog wristwatch that can match this accuracy - they are all far far worse. (Isn't it shocking that all those super-expensive Rolexes and whatnot are all going off by minutes per month!) Get one of the Casio watches that syncs to atomic clock radio signals every night - it will be second-accurate all the time.

Maursault 4y ago
> But was impressed when I learnt that there is no analog wristwatch that can match this accuracy Seiko 5 automatics apparently[1] can.[2] [1] https://www.watchuseek.com/threads/seiko-5-is-pretty-accurate.410417/post-5522035 https://www.watchuseek.com/threads/seiko-5-is-pretty-accurat... [2] https://qr.ae/prvf6L https://qr.ae/prvf6L
- klodolph 4y ago
  According to the linked thread, the Seiko 5 is an order of magnitude worse… 5 seconds per day, versus 15 seconds per month for a quartz watch.
  - Maursault 4y ago
    This one? 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...

chinabot 4y ago

It will be calibrated for room temperature, temperature changes do affect the oscillator frequency that is why highly accurate frequency sources have an "Oven" to keep the temperature stable https://en.wikipedia.org/wiki/Crystal_oven https://en.wikipedia.org/wiki/Crystal_oven