Time Formatting and Storage Bugs - GPS Date Rollover

GPS Date Rollover

In the last few months before the year 2000, two other date-related milestones occurred that received less publicity than the then-impending Y2K problem.

The first problem was related to GPS devices: GPS dates are expressed as a week number and a day-of-week number, with the week number transmitted as a ten-bit value. This means that every 1,024 weeks (about 19.6 years) after 6 January 1980 (the GPS epoch), the date resets again to that date; this happened for the first time on 21 August 1999. To address this concern, modernized GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137.