[time-nuts] What is NIST "official time" ?

Thu Aug 4 21:05:34 UTC 2011

I've seen similar issues when trying to compare time from differences
sources:

	At the same instant (simulated from deltas to a reference):

	1. Casio EDB-700 wristwatch:             11:35:00
	2. Computer clock                        11:34:57 (unadjusted)
(at this point I ran nistime-32bit.exe, available from NIST at
http://www.nist.gov/pml/div688/grp40/upload/nistime-32bit.exe)
	3. Computer clock, nist'ed               11:35:00
	4. Z3801, GPS Time                       11:35:15
	5. Z3805, UTC Time                       11:35:00
(here I set my PC time to 10min 30sec slow, eq. to 11:24:30 to catch fake
UTC-labeled time that actually is based on computer time)
	6. www.time.gov                          11:35:00
	7. Cell call to (303) 499-7111           11:35:00
	8. http://time.is/UTC                    11:35:00
	9. iphone4 small time at top             11:34:58
     10. iphone4 'UTC time' free app           11:34:58
     10. iphone4 'Emerald time' free app'      11:35:00
     11. www.csgnetwork.com/multitimedisp.html 11:24:30 
     12. Garmin GPS V before lock              11:30:52
     13. Garmin GPS V locked                   11:35:00
     14. leapsecond.com/java/gpsclock.htm	     11:24:30
     15. tycho.usno.navy.mil/cgi-bin/timer.pl  11:35:00
     16. ebay time (via Auction Sentry)        11:35:00

	While I haven't gone to extremes to measure the offsets in ms
(someone with more time in their hands could), there were very small
differences (one or two tenths of a second at most) between most displays.
Z3801 PPS on the scope and Casio display were pretty much in sync, too. Most
are good enough to debug the alleged 20s difference, which might be a result
of getting UTC from websites that actually just convert computer clock to
UTC. Both csgnetwork and leapsecond spelled that out, but often from the
Google search to the time display we don't bother with the fine print.
	Apple and all it's might ($76E9 cash reserves) has time 2s slow -
maybe AT&T is to blame - anyone can test a Verizon iphone? "Emerald Time"
app is great, shows delays from NTP servers, display time to tenth of a
second, seems accurate. The "UTC time" free app (by Mike Wells) seems to be
based on OS time, even though the Droid app with same name (from bjg222)
does the real thing (like Emerald Time app).
	Old Garmin 5 was minutes off (hasn't been used in months), but once
it acquired satellites it changed display very much in sync with the Casio
watch.

	Interesting the number of time sources we have at our hands,
nowadays (NTP, web sites, nist app, gps, WWVB, phone call, cell phones,
etc.)

Jose

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Christopher Quarksnow
Sent: Thursday, August 04, 2011 11:09 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] What is NIST "official time" ?

Actually I was in Seattle yesterday looking at a SkyScan "atomic" clock, and
it agreed with NIST time.gov applet, yet I was thrown off by some
Android-based applications such as Sidereal or TAI Clock and Converter, that
display "UTC", whereas it is apparently Android system time.
Whereas Android system time has been GPS-disciplined for about two years
(bug 5485), very few "smart" phones overcame the issue. Also most Android
ntp-based applications that I used until recently under Android 2.2 did not
work with 2.3 and that's the reason I used Sidereal or TAI Clock and
Converter. I finally resorted to UTC time, that truly retrieves UTC via ntp,
and now back in NY last night, all seems fine, except that Google, OHA and
other parties involved (who were informed of the Android bug way back)
should make sure that no one displays "UTC" in any Market application unless
it's derived from a relevant source.
It's dangerous enough that a good portion of Android phones are 15 seconds
fast, even though a carrier like Sprint is sending a pretty accurate UTC
stream even to basic phones.

Thanks to all,

Christopher

On Thu, Aug 4, 2011 at 12:02, Chris Albertson
<albertson.chris at gmail.com>wrote:

> On Thu, Aug 4, 2011 at 7:16 AM, Christopher Quarksnow
> <cquarksnow at gmail.com> wrote:
> > Wondering whether anyone can clarify what discipline the Boulder, CO
NIST
> > facility is broadcasting (or showing on time.gov) and qualified as "The
> > official U.S. time".
> > It appears to be about 20 seconds slower than UTC
>
> I think something must be wrong with the way you are measuring.
> Propagation can't time add 20 seconds  Can you explain exactly what
> how you are measuring.
>
> Chris Albertson
> Redondo Beach, California
>
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>

  I was actually in Seattle looking at a SkyScan clock that concurred with
NIST and now back in New York today, seems I had an issue with Android
Sidereal software that claimed UTC, yet derived such UTC value from Android
system clock. Whereas I thought that the Android system clock was right
(namely Android bug 5485 was offset in the phone I was using), it actually
was not. I have alerted the author of sidereal software.
There seem to be a transition issue
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