[time-nuts] GPS message jitter (was GPS for Nixie Clock)

[Mark Sims]

A lot of GPS receivers either don't support the ZDA message, or turn it off by default.  And many (most?)  that do send it send the time with  millisecond resolution.

The NMEA sentences for sending date and time were very poorly thought out.  Several different sentences can contain the time (maybe the same time in different sentences with a group,  maybe each sentence has a different time).   Only the ZDA and RMC sentences have the date.  There is no sentence with unified time/date, position, and velocity info.

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> So for a GPS or a timing unit on a NMEA-0183 bus, do they report their best
estimate of time to the nearest 10ms when the packet is sent? (since a PPS
line isn't shared)