[time-nuts] Striking change in iPhone time accuracy with 8.2

Dave Martindale dave.martindale at gmail.com
Wed Apr 1 09:18:59 EDT 2015

Hmm.  I'd say that the time setting accuracy may have improved, but the
timekeeping accuracy still isn't wonderful.

I just checked my iPhone, using the Emerald Time app to display the
difference between iOS time and NTP time.  The local time was 850 ms fast.
Then I went to Settings->General->Date and Time and turned "Set
Automatically" off, then back on again.  This seems to have forced the
phone to resync its local time, and now the error is zero (less than 1 ms).

I also have an iPad which had been configured not to set the time
automatically.  It was 2.5 seconds fast.  When I turned automatic setting
on, it reset its local time to within 2 ms of correct.

So the setting appears to be nice and accurate.  But the iPhone, which has
been in "automatic time set" mode ever since the iOS update 3 weeks ago,
was nearly one second off.  I don't know how often iOS does a time sync, so
I don't know how long it took to drift by that much.  This amount of error
does suggest that it only periodically resets itself to the correct time,
without trying to correct the local oscillator to provide continuously
accurate time (like using NTP would do).

- Dave

On Tue, Mar 31, 2015 at 11:59 PM, Anthony G. Atkielski <
anthony at atkielski.com> wrote:

> Has anyone else noticed a dramatic improvement in the accuracy of time
> of day on iPhones and iPads since the release of iOS 8.2? The accuracy
> used to be only plus or minus 2 or 3 seconds, now it is about 100
> times better, usually a few tens of milliseconds. I figure Apple might
> have finally paid some attention to accurate time of day with 8.2,
> possibly because of the Apple Watch. It's a pleasing improvement, I
> hope it's permanent.
> --
> Anthony
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