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Lu,

Wife's AT&T phone also is slow on time.gov and time.apple.com.
Interestingly, both phones show the exact same time, best as I can
determine.  So it's the AT&T network clocks.  I'm out in the
boondocks (SW Virginia), and they're not competing for service here
due to old partnerships.  Might explain the greater inattention to
clocks in SW Virginia (~50 seconds slow) than in San Francisco (3-5
seconds).

Fired up WWV just for yucks and the computer was correct, as
indicated already.

Fred

On Apr 22, 2008, at 9:45 PM, Lu Abel wrote:

>
> Wow!
>
> I guess I stand corrected on cellphones telling time.   I live in the
> San Francisco area and work in high tech.  Just polled a bunch of my
> friends who have AT&T service; they report that their phones are 3
> to 5
> seconds slow as compared to either time.gov or Unix NTP.
>
> AT&T now runs GSM (the cell phone scheme used in most of the world
> except the US), so I wonder about T-Mobil (the other major GSM
> vendor in
> the US).
>
> At the same time, I wish I knew more about GSM so I could
> understand how
> it sends time to phones.  50 seconds slow sounds like a LOT!
>
> Lu
>
> Fred Hebard wrote:
>> On a mac, using time.apple.com.  Just synced, and still about 50
>> seconds slow.
>>
>> On Apr 22, 2008, at 6:12 PM, Lu Abel wrote:
>>
>>
>>> Fred:
>>>
>>> I'm not an expert on cell phone technologies, but it may be that
>>> AT&T is
>>> the one provider that may not need accurate timekeeping to make its
>>> particular technology work.
>>>
>>> When you say you're on a network time server, are you on a Windows,
>>> Mac
>>> or Unix machine?   Windows only resynchronizes the computer's
>>> time-of-day clock with an NTP server once a week (or even less
>>> frequently);  I've seen at least one of my computers drift
>>> considerably
>>> in between.   I just checked my new Vista PC computer's clock
>>> against
>>> time.gov, it's three seconds slow with a resynchronization
>>> scheduled for
>>> Friday.   But it could just as easily be fast, as yours might
>>> be.   I
>>> personally have a lot of faith in time.gov (especially with a
>>> broadband
>>> connection) because it attempts to measure and compensate for any
>>> network delay.
>>>
>>> Wait, I forgot that I also have one of those digital clocks that
>>> synchronizes itself to the low-frequency time signal broadcast by
>>> WWVB.
>>> It appears to be between 0.3 and 0.5 seconds slow as compared to the
>>> www.time.gov display on my computer.   On the other hand,
>>> considering
>>> that it cost me all of $6, I have to wonder whether its time
>>> display is
>>> more or less accurate.
>>>
>>> Lu
>>>
>>> Fred Hebard wrote:
>>>
>>>> I followed up on this when it was mentioned previously on this
>>>> list,
>>>> and I believe the accuracy of cell phones may vary with the
>>>> network.
>>>> I'm on AT&T, and my impression is that the time is not
>>>> accurate.  For
>>>> instance, my phone now says it's 9:51:55 and my computer says it's
>>>> 12:52:42.  The computer is getting its time from a network time
>>>> server.  These may be more accurate than the USNO site, but, I
>>>> don't
>>>> know this one way or another.
>>>>
>>>> Fred Hebard
>>>>
>>>> On Apr 22, 2008, at 11:56 AM, Lu Abel wrote:
>>>>
>>>>
>>>>
>>>>> Bill:
>>>>>
>>>>> The time difference between your Garmin and the USNO web site is
>>>>> likely
>>>>> due to network delays (ie, the USNO sends you a time pulse at the
>>>>> correct time, but it takes almost a second to arrive at your
>>>>> computer).   The other web site run by USNO, www.time.gov, says it
>>>>> attempts to measure network delays and compensate for them.
>>>>> Another
>>>>> source for accurate time is your cell phone.  Mine only keeps
>>>>> time to
>>>>> the minute, but it very accurately rolls over at the 60-second
>>>>> mark.
>>>>>
>>>>> Lu Abel
>>>>>
>>>>> Bill wrote:
>>>>>
>>>>>
>>>>>> The current discussion on time, relativity and leap seconds
>>>>>> is, in
>>>>>> many
>>>>>> areas, well above my head.  Noting the various flavors of UT
>>>>>> (currently), an
>>>>>> observation and a pragmatic question for cel nav.
>>>>>>
>>>>>> The seconds readout between my GPS (Garmin GPS 76) and
>>>>>> http://tycho.usno.navy.mil/cgi-bin/anim
>>>>>> differ by about one (1) second.
>>>>>>
>>>>>> The web site (dial up modem at the moment) is nominally one (1)
>>>>>> second
>>>>>> behind the GPS readout.
>>>>>>
>>>>>> Bringing it into the realm of traditional navigation, which time
>>>>>> do I use to
>>>>>> set my hack watch? ;-)  Potentially a quarter mile intercept
>>>>>> difference
>>>>>> under ideal circumstances.
>>>>>>
>>>>>> I do not have access to a time-signal radio now.
>>>>>>
>>>>>> Bill
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>
>>>>
>>
>>
>>
>>>
>>
>
> >



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