> Many GPS receivers do have a 1 PPS (pulse per second) output
> that is quite suitable for this.
>
> The actual UTC time is generally provided as an NMEA signal,
> which is async at 4800 bps.  It's pretty easy to parse the data.

Thanks. It's been suggested to me (by someone at retail level) that
sometimes the GPS might be turned off. Can't see why that would
be, especially as this is a large ship. It has 11 clocks spread over
the ship, which gives you some idea. If that's the case I think I'll
use the GPS as the primary source and a kitchen clock oscillator
(generally stable to a minute or two per year) as the secondary

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