
LeapSecond – A web site dedicated to precise Time and Frequency - Tomte
http://www.leapsecond.com/
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jpeg_hero
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.

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saagarjha
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?

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giobox
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.

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klodolph
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.

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kuroguro
I wonder why phones don't use GPS to sync clocks? Or do they? Hmm...

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saagarjha
Phones usually just use network time, because the GPS is an expensive
component to spin up.

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MrEfficiency
Can you explain 'spin up'?

Do you mean that its Power/battery intense?

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saagarjha
Yup. The GPS drains battery.

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ape4
But when GPS is going for another purpose phones could grab the time. Don't
know if they do.

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ryandrake
Initial GPS signal acquisition is power intensive, but if it is already
tracking, then there should be no incremental cost to read the time
information.

GPS time tends to be very precise as well. In the NTP world, (simplifying
greatly) GPS can serve as a reliable “stratum 0” time source which feeds
stratum 1 servers, which go on to feed the rest of the NTP network.

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dfox
Building accurate NTP stratum 0 GPS time source is somewhat nontrivial
endeavour. Which explains why most of stratum 1 NTP timeservers (typically GPS
based) give wrong time (with error on the order of 500ms).

