GPS and The End of Week (EOW) Rollover “Problem”--Hype

> Lawley > Weird > GPS

This info is directly from email.

X-From_: owner-birding-aus@deakin.edu.au Sun Apr 25 08:33:28 1999
Date: Sun, 25 Apr 1999 10:28:40 +1000
From: Paul Taylor <birder@ozemail.com.au>
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To: Birding-Aus <birding-aus@deakin.edu.au>
Subject: Re: birding-aus Navigation device risk.
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> Paul Walbridge wrote:
>
> Hi all, this article appeared in saturdays Courier Mail in Queensland and
> could of some concern to fellow Atlassers.
> NAVIGATION DEVICE RISK
>
>
> " Hikers, fishermen and sailors who rely on electronic navigation could
> find themselves lost on August 21 because of a bug in the global position
> satellite system.
> The American-built satellite network calculates the date by counting the
> weeks since it was set up in January 1980.And when the counter hits 1024
> weeks, it is programmed to restart at zero.
> Warren Entsch, parliamentary secretary to the Minister for Science and
> Industry, yesterday warned that the zero date could cause some GPS
> recievers to look for satellites in the position they were nearly 20
> years ago."
>
> My concern is, is there any truth in this or is it just another one of
> those political beat-ups emanating from one of those paranoid American
> Congressmen or Senators.

The GPS End of Week (EOW) rollover "problem" occurs every 20 years or so (1024 weeks), though this is the first time it has happened since GPS came into existence. The GPS satellites will *not* be affected by this or the Year 2000 (Y2K) problem.

It is possible that some receivers (particularly older models) may have a problem and require a firmware upgrade or some other action to correct it; in many cases, a "cold start" initialisation is all that is required.

Check with your manufacturer if you have any concerns.

Some links to GPS manufacturers' web pages on the subject:

GPS Manufacturers -- The Sustainable Development Reference Link

• Garmin
  • Marass has a copy of the information
• Magellan -- Y2k
• Eagle
• Lowrance -- Year 2000 and Epoch Rollover Statement
• Trimble -- Y2k and Week Number Rollover

Unfortunately, there is so much hype about the Y2K problem at the moment that the media go into a frenzy about any possible date problem without doing their research. For example, "9/9/99" is a frequently quoted date. The value "9999" was often used in COBOL programs to indicate end-of-data; the date 9/9/99 is coming up, so the computer systems are going to break!

Wrong - if you consider other dates that have already passed, for example 1/11/98 and 11/1/98, you can see that storing them without zeroes would be extremely foolish. 9/9/99 is no exception, and would be stored as "090999" or "990909" - not "9999". I'm surprised we haven't heard more about the "odometer rollover problem" and other modern day numerology.

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Paul Taylor Veni, vidi, tici -
birder@ozemail.com.au I came, I saw, I ticked.

[And again: on 9 August 1999]

While most people have heard of the Y2K "bug", the GPS EOW (End-Of-Week) rollover is much less known. Whereas Y2K is alleged to cause problems when 2-digit year values roll over to "00", the GPS EOW rollover is where the 10-bit week counter (0-1023) rolls over to 0 again; this will occur at midnight 22 August 1999 UTC/GMT (= 10am AEST 22 Aug 1999.) Just like Y2K, it has never happened before, so there has been some media hype about the potential effects of the "problem" (planes falling out of the sky and other such nonsense.)

The good news is the EOW rollover is unlikely to have any significant impact on birders. If you haven't checked to see what (if any) action is required for your unit, now is the time to do so. The following are links to the common GPS manufacturers web pages on the subject (and Y2K):

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Joe Mehaffey's and Jack Yeazel's GPS Information -- Best Overall Source