Yo Achim! On Tue, 07 Feb 2017 20:36:15 +0100 Achim Gratz <strom...@nexgo.de> wrote:
> Gary E. Miller writes: > >> That slot should represent the number of useful bits. > > > > Yup. And in Selsky's case he really does have -30. > > Nope. I disagree. > The resolution of the numbers is 1ns, the useful digits aka > precision of the measurement doesn't extend that far down. That -30 > would be equivalent to 931ps, -29 is 1.8 ns, and I claim that -30 (931 ns) is closer than -29. > which is completely implausible. I'll > give you 30ns tops, that would be -25. You supposedly can get down to > about half that, but it needs another atomic clock as a reference. In the past I would agree with you, but no longer. And either way, -25 or -30, that is way closer to the truth than the current -20. And since ntpd does not even use the precision it is not worth arguing. > http://www.allanstime.com/Publications/DWA/Science_Timekeeping/TheScienceOfTimekeeping.pdf > https://ilrs.cddis.eosdis.nasa.gov/docs/timing/gpsrole.pdf > > The on-the-tin specification for GPS is 1µs, and that gives more or > less exactly the -20 that the receiver reports, not so mysteriously > after all. That is a way old spec. 20 years old. HP does not even exist anymore. Look at something more modern. Meinberg claims 50 ns for one product: https://www.meinbergglobal.com/english/products/pci-express-gps-clock.htm Parts like the ublox 8T claim better, < 20 ns accuracy: https://www.u-blox.com/sites/default/files/products/documents/NEO-LEA-M8T-FW3_ProductSummary_%28UBX-16000801%29.pdf So -30 can not be too far off. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin
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