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GPS Week Number Roll Over Advisory

October 22, 2018
Ottawa, ON


The GPS Week Number Roll-over Issue
The Global Positioning System (GPS) broadcasts time and date information. This includes a 10-bit week number (0 to 1023) relative to Jan 6, 1980. The maximum number of 1023 means this number resets or “rolls over” back to 0 approximately every 19 years and 35 weeks. The week number previously rolled over in August 1999, and will again on April 6, 2019. GPS receivers that do not account for this rollover will effectively jump back in time about 20 years, which can cause instruments that use these receivers to stop working unless the instrument is programmed to expect and correct for it. Many GPS receivers shift this rollover event to some other date in the future, effectively deferring the date at which its week number rolls over to a future time that is specific to that particular receiver. This complicates the situation because the date at which a particular instrument is affected is dependent on which model of GPS receiver it uses.

How this affects instruments that use GPS receivers
Most instruments that use GPS to accurately timestamp digitized data or for other precise time synchronization purposes will stop working correctly if the date provided by its internal GPS receiver is suddenly set back nearly 20 years in the past due to receiver’s week number rolling back by 1024 weeks. If you have instruments with internal GPS receivers, it is important to have the manufacturer of the instrument provide you with detailed information about if and exactly when it may be subject to a GPS week number rollover issue. The instrument manufacturer should know what GPS receiver is used and should be able to determine if and when the week number will roll over. The instrument manufacturer can then advise what action to take. A firmware update, hardware update, or retirement or replacement of the instrument may be required to avoid operational outages.

How this affects your Nanometrics instrumentation
Several Nanometrics products use commercial GPS receivers to derive accurate time and date. This includes Centaur, Taurus and EuropaT digitizer models, as well as other instruments that contain digitizers such as TitanSMA/EA and Meridian. Nanometrics Libra L-band transceivers including Carina and Cygnus models also use GPS for precise time synchronization in satellite networks.

Some early serial number Taurus instruments are affected by the April 2019 GPS week number rollover. Some Europa-T, Libra I Cygnus and Janus models are affected in October 2019 or November 2021. Action is required to keep these instruments operating after these dates.

No other Nanometrics instruments are affected by GPS week number rollover until the year 2025 or later. For these products, firmware updates will be provided to prevent any issues before those future events. Keeping the firmware up to date on these Nanometrics instruments will avoid the future GPS week number rollover issues identified below.

For more information...
For details on specific instruments, please see the GPS Week Number Rollover Reference for Nanometrics Instruments that follows.

Here are some references for additional information on the impending GPS week number rollover.

If you wish further information, please contact your Sales Account manager or send an email to


Bruce Townsend
Chief Technology Officer
Nanometrics Inc.

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With over 35 years of experience, Nanometrics is a global award-winning company providing seismic monitoring solutions and equipment for studying natural and man-made seismicity. We deliver world-class scientific instrumentation, installation, and training services.