GPS Week number roll over may make some GPS clocks no longer work. Below is the Memorandum explaining the change and what it could mean to you or your GPS. SUMMARY: Critical Infrastructure (CI) owners and operators and other users who obtain Coordinated Universal Time (UTC) from Global Positioning System (GPS) devices should be aware of the GPS Week Number (WN) rollover events and the possible effect a GPS WN rollover event may have on the reliability of the reported UTC. The legacy GPS navigation message has a ten (10) bit parameter that represents WN. Thus, the WN parameter in the GPS navigation message “rolls over” to zero every 1024 weeks starting from 0000Z January 6, 1980. The next WN rollover will occur April 6, 2019. The IS-GPS-200H interface specification identifies both the ten bit WN parameter and the WN rollover events. A GPS device that conforms to the latest IS-GPS-200 and provides UTC should not be adversely affected. However, tests of some GPS devices revealed that not all manufacturer implementations correctly handle the April 6, 2019 WN rollover. Additionally, some manufacturer implementations interpret the WN parameter relative to a date other than January 5, 1980.These devices should not be affected by the WN rollover on April 6, 2019 but may experience a similar rollover event at a future date. For example, a particular GPS device may interpret the WN parameter relative to a firmware creation date and would experience a similar rollover event 1024 weeks after that firmware creation date. https://ics-cert.us-cert.gov/sites/...GmH7lEZSwcvO4KeiFjEK5E6zJfyo4JE017O2yWs-kJDpg
