SATELLITE SYSTEM MUST RESET OR FACE TROUBLE The calendar for the global positioning system (GPS), which counts time in weeks and seconds, is expected to run into problems on Saturday when it rolls over to zero instead of moving to 1024. The system keeps track of dates by counting weeks, which makes it efficient but also limits it to 1,024 weeks. Saturday, August 21, 1999, will be the beginning of the 1,024th week since the system began operating on Jan. 6, 1980, and experts are not sure what the older individual systems will do when they have to roll over their calendars. Receivers could be affected by becoming non-operational, generating bad data, displaying 1980 dates, or spending hours attempting to lock on to the signals. Experts say that more than 90 percent of the estimated eight million military and commercial GPS receivers will experience no difficulties. The number of GPS receivers affected by the rollover will be limited primarily because most of the industry's growth has occurred in the past five years, after the problem had been identified and equipment was made to address the issue. (New York Times 08/16/99)