In message: <[email protected]> Magnus Danielson <[email protected]> writes: : Poul-Henning Kamp wrote: : > In message <[email protected]>, "Richard B. Langley" writ : > es: : >> <http://gauss.gge.unb.ca/ITU_future_UTC_(CGSIC_49th).pdf> : > : > Thanks. : > : > Although I do appreciate what the context conveys, I did smile when I : > noticed that the last slide mentions "GPS time" but ends with : > "Only UTC can be disseminated". : > : > I don't know if GPS or POSIX time is the most diseeminated timescale, : > but I suspect they both beat UTC by an order of magnitude when it comes : > to number of receivers... : : Almost every GPS receiver also applies the UTC corrections to produce a : UTC time. Infact, many of them can't externally produce any other time : than UTC. Some has the ability to deliver GPS time or UTC time. Only a : fraction of the receivers made only use GPS time, but then for some : specific use. : : So it is UTC and not GPS you should compare.
Ummm... Every GPS receiver calculates GPS time. Most are able to produce UTC time. But only after they "warm start" or after they get the UTC offset from the almanac. What they do before that is somewhat ill defined on some, over defined on others. Until they have this data, they can't start producing real UTC time. 12.5 minutes is the figure that's normally given for this. If you have a failure and have to swap in a new GPS receiver, you'll not have UTC time for at least 12.5 minutes (usually more like 15-20 minutes when all is said and done). A 12.5 minute down time means your annual reliability can only be 4 9's, not 5 9's... This is why many receivers remember the last UTC offset values and warm start with them if they have only been off a short period of time... Warner _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
