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Technology Stocks : 2000 Date-Change Problem: Scam, Hype, Hoax, Fraud
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To: Bill Wexler who wrote (612)4/14/1998 10:38:00 PM
From: Bill Ounce  Read Replies (1) of 1361
 
Mr. Bill Wexler, You are repeatedly stating information that conflicts with with the official sources of authority for the NavStar GPS

It is -indeed - a "non issue" since the EOW has absolutely no bearing in calculating current position. A very old unit may display the wrong calendar date as a result of EOW miscalculation. A relatively trivial problem.

The US Air Force, who maintain the NavStar GPS system, say that "GPS End of Week (EOW) Rollover may cause a 'crash' of a receiver/system."
(http://gps.laafb.af.mil/y2000/rollov.htm)

The US Navy states "Some receivers may display inaccurate date information, some may also calculate incorrect navigation solutions."
(http://tycho.usno.navy.mil/gps_week.html)

the facts -- as I understand them
The GPS uses satellites with orbit altitudes such that the satellites repeat the same track and configuration over any point approximately each 24 hours (4 minutes earlier each day). An identical, time-of-day derived, pseudo-random number stream, produced simultaneously by all satellites and receivers, is used for triangulation purposes and receiver clock synchronization purposes.

GPS receivers use a 10-bit field to calculate the system date, based on an offset since January 1980. Every 19 years, the field resets to zero as specified by the design. Poorly designed receivers did not take this in to account and after August 22, 1999 may incorporate an invalid basis week in their calculations. The unit may become confused, which is why the government GPS sites give the warnings that they do.
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