[LEAPSECS] Crunching Bulletin B numbers (POSIX time)

Warner Losh imp at bsdimp.com
Wed Feb 23 13:05:58 EST 2011

On 02/23/2011 03:57, Ian Batten wrote:

>> Having a known list of leap seconds let one recover TAI time from a cold GPS receiver in a few seconds to a minute, rather than waiting ~20 minutes for the almanac to download.

> You may operate on computers on which adding 19 is a hard problems, but most of us can manage it in our heads. "GPS Time" is TAI-19. Recovering UTC is a harder problem, although I'm not sure I buy your scenarios as being ones that the rest of us need to worry about (operating Loran stations as a reason to hold the rest of us to ransom?)

It is but one example of a system that has cold spares. There are
others, and this is a simple, easy to understand example.

> And given how cheap GPS receivers are, why not operate a warm spare as well as a cold spare?

There is an independent gps receiver that's operated, so usually a gps
failure just switches over to the hot spare. However, if there's an
event (or series of events, like operator error) that takes them both
out, you have to come up on the cold spare.



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