Warning Given on Navigational Device Glitch

Several federal agencies issued a warning Thursday to hikers, boaters, drivers and others who use the global positioning system to beware of the possibility that their devices may malfunction Aug. 21-22 because of an unusual phenomenon known as “End of Week Rollover.”

The rollover problem stems from the original design of the GPS, which calculates the date by counting the number of weeks from Jan. 6, 1980. After the 1,024th week--about 20 years--the system resets back to zero.

The date resetting could make some models of the popular navigational device stop working or display inaccurate positions, times and dates.

The government has been aware of the rollover issues since GPS was created, and its navigational systems have all been repaired and tested. But some consumer devices and commercial systems are vulnerable.

John Lovell, director of quality for Trimble Navigation Ltd., the leading maker of GPS devices, said that most consumer products, which have been on the market for only the last three to five years, will not have any serious problems.

He added that those that do will probably only show an incorrect date. A navigational error would be much rarer since GPS uses the time, not the date, to calculate a position, he said.

“There’s a very small chance for a navigational error, but not zero,” Lovell said. “Everyone should check with the manufacturer to make sure.”

Neil Ashby, professor of physics at the University of Colorado at Boulder and a specialist in the global positioning system, agreed that there will be few serious problems.

“Most of the companies are aware of this and have taken steps to avoid it,” he said.

The federal warning was put out by the Consumer Product Safety Commission, the Department of Transportation, the Interior Department, the Agriculture Department and the Federal Trade Commission.