The bug is likely to only hit a small number of GPS devices, but for those impacted the results could be severe, resetting the receiver’s time and corrupting its location data.
The advice is that if you’re just using a commercial device the fix is quite simple: just check that its software is up to date.
TomTom has warned customers to update its gear. Garmin says it’s been testing its devices for problems but that “the vast majority of Garmin GPS devices will handle the event without issues”.
And an official memorandum from the Department of Homeland Security says any GPS receivers running the latest IS-GPS-200 standard and connected to UTC “should not be adversely affected”.
The rollover issue itself is caused by the fact that GPS systems count weeks using a ten-bit parameter. This means they start counting at week zero and reset when they hit week 1,024. The first count - or “GPS epoch” - started on 6 January, 1980, and the first reset took place on 21 August, 1999. That means the next one is due 6 April this year.
When the rollover happens, older devices may reset their date, potentially corrupting navigation data and throwing off location estimates. GPS relies on precise timing data to operate, and each nanosecond the clock is out translates into a foot of location error.
While the next GPS week reset is scheduled for 6 April, actual errors might kick in later as an affected receiver won’t start outputting erroneous data until long afterwards.