[tz] GPS Week Number Rollover Apr 6/7

[Brian Inglis]

Expect some amount of time related disruption around April 7 00:00 GPS as the
GPS 1K week cycle rolls over and GPS receivers that have not been patched or
updated to use new CNAV and MNAV messages, or compensate for not doing so,
provide incorrect time, position, and navigation solutions.

Garmin, for example, rolled out updated firmware for some of their receivers,
including the 18x popular on NTP servers, just over a week ago.

Previous rollovers have shown symptoms of clocks being out by multiples of 256
weeks, some resetting to the GPS epoch at 1980 Jan 06 Sun 00:00:00+0000, showing
misleading position and navigation solutions, depending on what inputs are used
to solve the 4D simultaneous equations.

Airlines, ships, and well maintained commercial trucks shouldn't crash, but the
rest of us should check any devices using GPS!

If my script is correct, the rollover occurs at the indicated instant on the
time scales below:

2019 Apr 06 Sat 23:59:42+0000  JD 2458580.499792  MJD 58579.999792  ToD 86382
NTP 3763583982  Unix 1554595182  GPS We 2048 Cy 2 Wn 0 Wa 0 ToW 0 DoW 0 ToD 0
TAI-UTC 37  TAI-GPS 19  GPS-UTC 18

[*NOT* an April Fools post, unfortunately!]

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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