3 ms·

Cool, but now I am looking up the cost of a “Kvarz Active Hydrogen master” When the Apple Watch first came out they made a lot about hoe precise it is. I wonde

Cool, but now I am looking up the cost of a “Kvarz Active Hydrogen master” When the Apple Watch first came out they made a lot about hoe precise it is. I wonder if that sounds still true, they’ve kind of dropped it from the marketing.

nategri 8y ago
Eh I'm guessing it's just not interesting to most people. Your phone/laptop is also a very precise timepiece but it's a feature you get "for free" in a modern OS, so not usually worth mentioning.
- klodolph 8y ago
  Your phone/laptop is not especially precise by modern standards. They are often nothing more than ordinary crystal oscillators, with frequency errors somewhere around 10 or 20 ppm (very roughly, sometimes worse, sometimes far worse--the Raspberry Pi is awful). You may intuitively think of this as "very precise" but these are not really much better than quartz watches made in the 1970s. Note that this is nowhere near precise enough that you would worry about leap seconds. Your computer might gain or lose 5 or 10 minutes every year, so leap seconds just get lost in the noise. Of course, you won't notice this due to NTP... but at that point, you're not really relying on your phone or laptop, you're relying on atomic time standards elsewhere in the world. If you had a TCXO (temperature-compensated crystal oscillator, relatively common in watches and RTCs), you could get better accuracy, maybe down to 0.5ppm or 20 seconds per year. These basically work by adjusting the oscillator in response to changes in temperature. This is on par with the best quartz timepieces available today (0.1-0.5 ppm), but still not accurate enough to worry about leap seconds. You can check the actual drift on Linux systems with NTP by running "cat /var/lib/ntp/ntp.drift", which shows you how many ppm your particular clock is off by. For me, I see a value with magnitude around 1.2, which is ~38 s per year. I can conclude that my motherboard probably has a TCXO because otherwise the drift would be larger. If you had an OCXO (oven-controlled crystal oscillator, note that the "C" is different), you could get down to 0.005ppm, or something on the order of 200 ms per year. At this point, observing leap seconds becomes mandatory. These work by maintaining the crystal at a predefined temperature using an oven. However, this takes up more space and requires more power, so it is out of the question for laptops or phones. (As a minor note, the very best modern mechanical "chronometer certified" watches are somewhere around 10ppm, making them worse than all but the worst quartz watches.)
  - bacon_waffle 8y ago
    Perhaps of interest: the Accutron 214 (released 1960) uses a tuning fork's ringing for both regulation and mechanical power, and was advertised to be accurate to 1 minute per month. They are reasonably easily obtainable, and are a great example of some really elegant engineering.
  - madengr 8y ago
    The problem is TCXO may have a 0.1 ppm temperature stability, but the initial accuracy is still 1 ppm, along with aging effects.
saagarjha 8y ago
I think a significant portion of that precision came from synchronizing with network time, did it not? Or did it run unusually precise even when disconnected from the network?
- giobox 8y ago
  This _almost_ seemed driven more by a desire to make sure the animated watch faces stay beautifully in sync when customers view the Apple Watches together in stores, which is a pretty cool little trick, that the watch itself is accurate is nearly a side benefit... I recall various Apple exec interviews at the original launch drawing attention to this.
  - klodolph 8y ago
    You can get accuracy well under 100 ms using ordinary NTP over the public internet, and I assume that since the Apple Watch has GPS that this is also used to synchronize the watches. All you need is an ordinary crystal oscillator and a GPS receiver, stitch it together with a little software and all your watches in the store are synchronized.
- LeoPanthera 8y ago
  Some people on the watchuseek HAQ forum determined that, even permanently disconnected from an iPhone and any network, it is accurate to ~10 seconds per year, which is extremely impressive.
  - planteen 8y ago
    That's about 3 ppm, which is pretty good. Based on that ppm value, my guess is a temperature compensated crystal oscillator. I imagine it was kept at room temperature for the duration of the test?
    - LeoPanthera 8y ago
      I'm afraid I don't know the details, but a TCXO was the conclusion, yes.

nategri 8y ago

Eh I'm guessing it's just not interesting to most people. Your phone/laptop is also a very precise timepiece but it's a feature you get "for free" in a modern OS, so not usually worth mentioning.

klodolph 8y ago
Your phone/laptop is not especially precise by modern standards. They are often nothing more than ordinary crystal oscillators, with frequency errors somewhere around 10 or 20 ppm (very roughly, sometimes worse, sometimes far worse--the Raspberry Pi is awful). You may intuitively think of this as "very precise" but these are not really much better than quartz watches made in the 1970s. Note that this is nowhere near precise enough that you would worry about leap seconds. Your computer might gain or lose 5 or 10 minutes every year, so leap seconds just get lost in the noise. Of course, you won't notice this due to NTP... but at that point, you're not really relying on your phone or laptop, you're relying on atomic time standards elsewhere in the world. If you had a TCXO (temperature-compensated crystal oscillator, relatively common in watches and RTCs), you could get better accuracy, maybe down to 0.5ppm or 20 seconds per year. These basically work by adjusting the oscillator in response to changes in temperature. This is on par with the best quartz timepieces available today (0.1-0.5 ppm), but still not accurate enough to worry about leap seconds. You can check the actual drift on Linux systems with NTP by running "cat /var/lib/ntp/ntp.drift", which shows you how many ppm your particular clock is off by. For me, I see a value with magnitude around 1.2, which is ~38 s per year. I can conclude that my motherboard probably has a TCXO because otherwise the drift would be larger. If you had an OCXO (oven-controlled crystal oscillator, note that the "C" is different), you could get down to 0.005ppm, or something on the order of 200 ms per year. At this point, observing leap seconds becomes mandatory. These work by maintaining the crystal at a predefined temperature using an oven. However, this takes up more space and requires more power, so it is out of the question for laptops or phones. (As a minor note, the very best modern mechanical "chronometer certified" watches are somewhere around 10ppm, making them worse than all but the worst quartz watches.)
- bacon_waffle 8y ago
  Perhaps of interest: the Accutron 214 (released 1960) uses a tuning fork's ringing for both regulation and mechanical power, and was advertised to be accurate to 1 minute per month. They are reasonably easily obtainable, and are a great example of some really elegant engineering.
- madengr 8y ago
  The problem is TCXO may have a 0.1 ppm temperature stability, but the initial accuracy is still 1 ppm, along with aging effects.

saagarjha 8y ago

I think a significant portion of that precision came from synchronizing with network time, did it not? Or did it run unusually precise even when disconnected from the network?

giobox 8y ago
This _almost_ seemed driven more by a desire to make sure the animated watch faces stay beautifully in sync when customers view the Apple Watches together in stores, which is a pretty cool little trick, that the watch itself is accurate is nearly a side benefit... I recall various Apple exec interviews at the original launch drawing attention to this.
- klodolph 8y ago
  You can get accuracy well under 100 ms using ordinary NTP over the public internet, and I assume that since the Apple Watch has GPS that this is also used to synchronize the watches. All you need is an ordinary crystal oscillator and a GPS receiver, stitch it together with a little software and all your watches in the store are synchronized.
LeoPanthera 8y ago
Some people on the watchuseek HAQ forum determined that, even permanently disconnected from an iPhone and any network, it is accurate to ~10 seconds per year, which is extremely impressive.
- planteen 8y ago
  That's about 3 ppm, which is pretty good. Based on that ppm value, my guess is a temperature compensated crystal oscillator. I imagine it was kept at room temperature for the duration of the test?
  - LeoPanthera 8y ago
    I'm afraid I don't know the details, but a TCXO was the conclusion, yes.