Don Jewell, GPS World, writes:

Since I have been writing about the Perfect Handheld GPS Transceiver, I have received numerous letters and emails asking why an atomic clock is necessary in a handheld transceiver, or in any device for that matter. I could write volumes on the subject, literally, but will try to boil it down to a few key concepts for you.

DRU SEFTON, Newhouse News Service, reports:

Let us now take 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of cesium-133 to pay tribute to the atomic clock.

That would be one second.

Fifty years ago this October, the atomic clock first became available commercially. It and its descendants use that cesium frequency to keep time, accurately measuring to one-billionth of a second.

GPS World reports:

The current GPS constellation — its health and viability — continues in question and under scrutiny, despite reassurances from the Air Force.

Last month’s GPS World Survey & Construction e-newsletter relayed user plaints that there aren’t enough healthy GPS satellites. Surveyors say they can’t use RTK a full day with the current constellation even with every satellite healthy — and that recently there have been more satellite outages than ever before. They’ve resorted to filling GPS gaps with GLONASS.

The online story drew immediate affirmation. “While most of the time we get good coverage, for the last couple months we have had a 4 to 6-hour gap where we ‘float’ a lot and our precision goes down. Unfortunately this gap is usually between 10 am and 2 pm, which creates some interesting scheduling problems.”


NO positive leap second will be introduced at the end of December 2006.
The difference between Coordinated Universal Time UTC and the
International Atomic Time TAI is :

from 2006 January 1, 0h UTC, until further notice : UTC-TAI = -33 s

Ron Cowen, Science News reports:

Did last New Year’s Eve seem a trifle tedious? Did your celebration go on a little too long? Maybe that’s because just before midnight Greenwich Mean Time—6:59:59 Eastern Standard Time to be exact—the international authority on timekeeping ordered everyone to wait a second. For the 23rd time since 1972, the International Earth Rotation and Reference System Service added an extra second to the time standard, a worldwide network of some 200 atomic clocks.

The clocks, most of them governed by the ultrasteady vibrations of electrons in cesium atoms, are accurate to a tenth of a billionth of a second a day. However, humankind’s oldest clock—Earth’s rotation—isn’t nearly so precise. Primarily in response to the moon’s tidal pull on the oceans, our planet isn’t turning quite as fast as it used to. To keep Earth time and atomic time in sync, experts have agreed to insert a leap second every few years into the official atomic-based standard, which is called Coordinated Universal Time.

Because the rate at which Earth slows isn’t perfectly predictable from year to year, leap seconds are announced only 6 months in advance. That’s a concern for software designers, operators of satellite-based systems, and anyone else who relies on split-second communications. Six months isn’t much warning for engineers who operate computer programs or types of equipment that require precise time information and are intended to last for at least a decade. Some operations, such as the Global Positioning System, use custom time scales that eschew leap seconds entirely.

A glitch in inserting a leap second, these researchers say, could throw everything off, whether it’s the timing of an international business deal, the location that a missile hits, or the star that the Hubble Space Telescope observes. “A 1-second hiccup in the phasing of North American power grids would likely cause a hemispheric blackout,” notes Daniel Kleppner, director of the Massachusetts Institute of Technology–Harvard Center for Ultracold Atoms in Cambridge, Mass., in the March Physics Today.

Inserting a leap second “is a little bit like walking along the San Andreas fault,” comments Tom Van Baak, a self-described precision-time hobbyist from Bellevue, Wash. It’s typically an innocuous experience, but there’s always the potential for catastrophe lurking beneath the surface.

With Earth continuing to grow more sluggish, scientists note, leap seconds will have to be introduced more and more frequently. “Eventually, you get to the point that the paradigm involved in this won’t work,” says Dennis McCarthy, a time specialist now retired from the U.S. Naval Observatory. “You’ve got to do something different. The addition of leap seconds is going to be an increasing nuisance for people who are counting on a time scale where a minute actually contains 60 seconds.”

That’s why a group of U.S. time-communication specialists, part of the International Telecommunications Union, proposed in 2004 to do away with leap seconds altogether. Let atomic time be out of whack with Earth rotation–based time, these scientists say. Their proposal is now under review by a working group of the union.

Poul-Henning Kamp, Slagelse, Denmark, writes:

When I contacted D-Link back in November 2005 about the way D-Link products abused my NTP-server, I expected to get in touch with somebody who understood what they were talking about, I expected them to admit that D-Link had made a bad decision and I expected that D-Link would make good on the damage they were responsible for.

For the last five months I have wasted a lot of time trying to reach some kind of agreement with the Californian lawyer which D-Link put on the case. I can’t quite make up my mind if D-Link’s lawyer negotiates in bad faith or is merely uninformed, I tend to suspect the latter, but either way, as of this morning I decided to cut my losses.

Since no one else at D-Link has reacted to my numerous emails, I have no other means of getting in touch with D-Link other than an open letter. I realize that it will be inconvenient and embarrasing for D-Link to have this matter exposed in public this way, but I seem to have no other choice.

I will now lay out the case below in such detail that any moderately knowledgeable person should be able to understand it, and hopefully somebody, somewhere in D-Link will contact me so we can get this matter resolved.

KAZINFORM reports:

LONDON. December 30. KAZINFORM - The world’s top timekeepers will insert an extra second—or leap second—just before midnight in coordinated universal time (UTC) on New Year’s Eve. (That’s the same as 6:59:59 p.m. eastern time on December 31.) UTC is determined by atomic clocks and is five hours ahead of eastern time.

Keith J. Winstein, The Wall Street Journal, reports:

What time is it when the clock strikes half past 62?

Time to change the way we measure time, according to a U.S. government proposal that businesses favor, astronomers abominate and Britain sees as a threat to its venerable standard, Greenwich Mean Time.

Word of the U.S. proposal, made secretly to a United Nations body, began leaking to scientists earlier this month. The plan would simplify the world’s timekeeping by making each day last exactly 24 hours. Right now, that’s not always the case.

Because the moon’s gravity has been slowing down the Earth, it takes slightly longer than 24 hours for the world to rotate completely on its axis. The difference is tiny, but every few years a group that helps regulate global timekeeping, the International Earth Rotation and Reference Systems Service, tells governments, telecom companies, satellite operators and others to add in an extra second to all clocks to keep them in sync. The adjustment is made on New Year’s Eve or the last day of June.

via Google’s cache of http://www.schriever.af.mil/GpsSupportCenter/archive/Frontpage/2004_j006_SVN23_Anomaly.htm as retrieved on 3 May 2006 00:45:57 GMT.

A significant GPS anomaly occurred on 1 Jan 04, beginning at approximately 1833Z. The anomaly affected precise timing and navigation users over large portions of Europe, Africa, Asia, Australia, and the far northern reaches of North America. (see Figure 1)

The anomaly was due to a failed atomic frequency standard (AFS) on SVN/PRN23. The GPS system relies heavily on the accuracy and stability of its AFS’. A failed AFS affects not only precise timing users, but can also significantly degrade navigation accuracy.

A lack of hard failure indications in satellite telemetry coupled with satellite visibility limitations in the Master Control Station’s L-Band monitor station network made this anomaly difficult to characterize and resulted in the transmission of Hazardously Misleading Information* between approximately 1833Z and 2118Z.

* Hazardously Misleading Information (HMI) – As defined in GPS Standard Positioning Service Performance Standard, October 2001, Page 14.