The Global Positioning System (GPS) has its own date and time scale based on counting weeks, and seconds within a week. However, the field that contains the week number is limited to 1024 weeks, a GPS rollover event occurs when this counter reaches week 1023 and then rolls back to week 0.
When does this happen?
About every 20 years. The upcoming GPS week rollover event is on April 6th, 2019.
Has this happened before?
Yes, this is the second event. GPS week zero was in January 1980. The 1024 week counter ran out and rolled over for the first time on August 21, 1999
What is the result of this if my product is affected?
Typically affected products will still show correct position, but will show incorrect date and time. In extreme cases position may be affected.
Simrad has carried out extensive testing on all current products, all previous generation products and a significant number of legacy products. The result of these tests ensure that our customers have the best information available on this issue. In cases where we have found an incompatibility we have issued a software update, when possible.
Is my Simrad product affected?
No currently available Simrad products have any known issues with GPS week rollover. This is the 2nd week rollover event so – as a general rule – our GPS chipset suppliers were aware of the issue and had this covered in their test and validation plans for more recent chipset designs.
