The GPS Week Rollover is an event which the GPS Satellite system resets the counter for the week number, thus affecting the calculation of the current date. This occurs every 1024 weeks (~19.7 years). Most GPS receivers have adapted and have firmware to correctly calculate UTC time and date. Older GPS receivers may not accommodate this reset and could result in a direct impact on using the Coordinated Universal Time (UTC), and possibly affect the location reported by the GPS receiver.

The GPS Week Number parameter is a ten-bit value in the range 0-1023, repeating every 1024 weeks. Week 0 started at 00:00:00 UTC on Sunday, 6th January 1980, so the week number 'rolled over from 1023 to 0 at 23:59:47 UTC on Saturday, 21st August 1999. This week number rollover will occur again on the 6th April 2019.

The US Department of Homeland Security have released a memorandum titled “U.S. Owners and Operators Using GPS to Obtain Time,” which is intended to provide an understanding of the possible effects of the issue.

Action:  ACR has taken measures to verify that the GPS Week Rollover WILL NOT be an issue with our recent products listed in this SIL. These products are not adversely affected by the GPS Week Number Rollover and will operate as designed. The method of verification was established by GPS receiver vendor declaration, product testing, or initial product certifications.

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