I have received a 'Notice To Mariners' from the Maritime & Coastguard Agency (MCA) as follows :
The MCA has issued a special safety bulletin to all mariners who use older GPS following a so-called 'week number rollover' event on 6th April 2019.
All GPS systems count time in weeks from 6th January 1980. The week number is stored as a 10-bit binary number which only allows for a maximum of 1,024 weeks before resetting itself to 0 (Zero). This rollover happened 6th April 2019 and all GPS receivers and systems using GPS Chips for both position and UTC which are 10 years old.
If it affected your GPS will show an incorrect date &/or time.
The US Department of Homeland Security has reported an error of one nano-second in the time equates to one foot of position error.
One Nano-second is one thousand -millionth of a second.
It wouldn't take much time difference/error to be a few miles off course.
I know there have been a couple of threads recently about weird dates / times on 'old' GPS systems - this may be the answer.
