GPS Week number is a number that helps GPS devices figure out what day it is. Imagine you have a calendar at home, with each day marked on it. Now, let's say you have a friend who lives across the country, but they have the exact same calendar as you do. If you want to make plans to meet each other on a certain day, you need to make sure you're both looking at the same day on your calendars.
GPS satellites work the same way. They have a calendar that helps them know what date it is. But instead of using the same calendar as everyone else, they have their own special calendar that starts counting from January 6th, 1980. Every 1,024 weeks, the GPS Week number resets to zero and starts counting again. This means that every 1,024 weeks, or about every 19.7 years, there is a "rollover" of the GPS Week number. The next such rollover is expected to occur in April 6th, 2019.
So, why does this matter? Well, if GPS devices don't correctly account for the GPS Week number rollover, they may start giving incorrect dates. This can lead to problems like incorrectly timestamped data, miscalculated distances, and time-based errors in GPS devices. This is why it's important for device manufacturers to update their firmware to account for the GPS Week number rollover, and why it's important for users to make sure their devices are up-to-date.