What to know about the GPS week counter rollover

This isn’t really a problem for new devices, which are now fitted with the latest software that can recognise when the global positioning system resets itself, and adjusts accordingly.

However, if your GPS receiver system is a lot older, it may not work properly after April 6.

The GPS system counts weeks from a start date of January 6, 1980. However, it can only count to a maximum of 1024 weeks – you might recognise that as a significant binary number, two to the power of 10 – after which it has to go back to zero.

If your older GPS receiver has not had any software update to help it reset the week counter, your device might be tricked into going back in time to the last time a rollover occurred – August 1999.

Most newer devices won’t be affected, just the older ones.

According to Errol Cain, the managing director of elctronics group Australian Marine Wholesale, many boaters still relied on older GPS equipment as their prime source of navigation, and should be concerned about the next date rollover.

"If your equipment is older than 12-15 years, I would suggest that now would be a good time to upgrade it to something current," Cain said.

"I liken equipment that is 12-15 years old as being the equivalent to keeping a 1980s Ford Falcon with more than a million kilometres on the clock roadworthy. A unit of this age is also five or six generations out of date.

"I often ask customers how their 12-year-old mobile phone is going."

Cain said a current 12.0-inch multifunction display was around 30 per cent cheaper than it was 14 years ago, with an increase in functionality of more than 80 per cent.

"A smaller 7.0-inch unit is even better value at only 25 per cent of the cost of a 12.0-inch unit with exactly the same functionality. Why you would pin you navigation and safety on such old (in electronics terms) equipment is beyond me."

That was the month that Brittney Spears’ “... Baby One More Time” was rocketing up the Australian charts. That’s likely reason enough not to want to go back there.

But significantly for the GPS system, the magnetic poles are on the move. Over the last few decades, particualry the north pole has moved so much that instead of the US-based National Oceanic and Atmospheric Administration officially updating where the pole sits via its World Magnetic Model every five years, it has had to update it a year earlier.

How much has the north pole moved? In the early 1900s, it was near Canada moving at about 10km a year. Today, it’s closer to Siberia and shifting fast – around 40km a year.

While an older device may have coped with the 1999 update, there’s no guarantee that it will cope with the April 6 one.

The Australian Maritime Safety Authority has warned that the internal clocks of some GPS systems will lose track of time and are likely to report the wrong time and location.

In some instances, the GPS receiver could simply stop working. AMSA warns that some GPS systems may already be affected.

Historically, the variation in true magnetic north can vary as much by 10s of degrees. Each degree of latitude is more than 100 kilometres on the ground.

If your device keeps working, it may show you as being somewhere very different to where the device is physically located. In a rescue situation, this could be very bad.

The easiest way to see if the rollover has dragged your device back to the 1990s is to switch it on and get a GPS coordinates reading.

Then it’s time to reach into your pocket and grab a smartphone. These have in-built GPS receivers used for setting the clock, navigation apps and other roles, such as capturing the geolocation of the last photo you took – it’s how Google Photos can sort your images by location when you ask it.

A modern smartphone is likely to be compliant with GPS ICD-200, a global standard that accounts for GPS system rollovers. Either use some GPS software to get your location, or turn on timestamps for photos and take one, and compare the numbers between devices.

They should match.

Cool your jets: the next rollover isn’t expected until April 6, 2038.