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Why GPS Rollover Matters


It’s like Y2K for Google Maps.

Owners of older GPS systems were advised last week to check their devices, as the then-upcoming GPS rollover could’ve caused some trouble with their systems’ dates and location, therefore rendering the device useless. Thankfully, no major malfunctions were reported. But what was this GPS Rollover, and why does it matter?

When Global Positioning Systems (GPS) were first implemented way back in the 1970s, the time and date functions were still defined by a 10-bit-number. This means that unlike a Gregorian calendar that uses year, month, and date, a GPS uses what we call the ‘week number’ (WN), which is shown as a 10-bit-number that resets to 0 every 1,024 weeks or approximately 20 years. Atomic clocks on satellites are set to this ‘GPS time.’ Their nature as satellite signals makes them very accurate, in addition to them being available almost anywhere on the planet. In fact, GPS systems from all over the world use them for their accuracy.

However, as mentioned above, the WNs shown in GPS systems are set to revert back to 0 approximately every 20 years. The first time this happened was on August 21, 1999. It caused some confusion with regards to location precision of GPS navigation systems, as that highly depends on the accuracy of GPS time.

This is why the US Department of Energy sent out warnings when it was scheduled to happen again on April 6. Thankfully, newer GPS models are already protected against this kind of thing happening – modern systems now use a 13-bit field, which only resets after 8,192 weeks or roughly 157 years.