Y2K? For GPS users, the problem is EOW

WASHINGTON, D.C. (July 22, 1999) — Users of equipment that relies on Global Positioning System technology should worry less about Y2K and more about EOW.

EOW stands for “End-of-Week” rollover, a phenomenon that occurs once every 20 years and will happen next on Aug. 21-22. The glitch may prevent equipment from locating GPS satellites, or cause it to display inaccurate positions, times, or dates.

EOW rollover occurs every 1024 weeks — about once every 20 years. The GPS system calculates time by counting the number of weeks since Jan. 6, 1980 — up to a maximum of 1023 weeks. At midnight between Aug. 21-22, 1999, the GPS week “counter” will roll back to zero weeks, and start calculating dates from Jan. 6, 1980, all over again.

Some newer GPS receivers have been programmed to solve the problem. Users are being urged to check with their receiver manufacturer to find out if it is EOW-rollover compliant.

The U.S. Dept. of Defense issued a statement saying that the constellation of GPS satellites itself will not be affected by EOW. The EOW problem also will not affect Qualcomm Inc.’s OmniTRACS satellite-based equipment-tracking products, widely used in the trucking industry, because the system does not rely on GPS.

The U.S Dept. of Transportation has posted a list of receiver manufacturers and contacts at the U.S. Coast Guard’s Web site.