NavList:

<<I'm a bit turned around by what you're asking for.  Are you looking for a timepiece independent of GPS to keep accurate time without an outside reference?  Even if HF and GNSS fail for some reason, the atomic clock time standards should be readily available via the internet.  You might only get concerned if you were away from such a reference for a long period of time, say a slow ocean passage of many weeks.  In that case, if you don't trust GNSS time, you'd need a chronometer.  The key with the chronometer isn't how absolutely accurate it is, it is that it has a constant error rate.  Most time pieces fail this test.  If you know that it takes a week for the clock to gain a second, you can project what time it is for any amount of time after your last reference.  For example, 4 weeks later, you will be 4 seconds fast.  The absolute accuracy of the clock isn't good, but you know how to correct it.>>

I'm looking for a self-contained time reference to use in the event of a loss of GPS.  I am presuming a boat that is not equipped with HF gear, because of the obsolescence of the shore stations on which it depends.

My real question is: what is reasonable, and is the standard answer of three Timexes really the best we can do?

I get it on the constant error rate.  I'm not sure that the error rate of the average cheap digital watch is as constant as is widely believed particularly when the watches are not stored at a constant temperature.  That approach requires regular checks.  Maybe having a ship's clock and a HAQ watch that are both accurate enough to use without rating would be a better answer given that they are available, compact, and low cost.  I'm thinkout out loud, I guess.