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    SubjectRe: [ntpwg] Bug: Status/Summary of slashdot leap-second crash on new years 2008-2009
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    On Jan 8, 2009, at 10:02 AM, M. Warner Losh wrote:

    > In message: <20090108104854.2dbc41b1@lxorguk.ukuu.org.uk>
    > Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
    > : > On FreeBSD, Solaris and Digital Unix, I'll point out, that jumping
    > : > backwards is used, and has been used since at least 1994. So
    > saying
    > : > it isn't used in the world today is flat out wrong.
    > :
    > : I stand by my comment - when was the last time the IERS used a leap
    > : second removal ? The code may exist but it doesn't happen.
    >
    > Jumping backwards is used for every leap second that IERS has ever
    > done, which was your original comment. There's has never been a case
    > where there was a leap second for jump forward though. The proper
    > technical term here is 'negative leap second'. All leap seconds up
    > until now have been positive leap seconds, and it is unlikely there
    > ever will be a negative one.

    I disagree. In the 1970's, the excess LOD was as much as 3 msec.
    After going down some, the mid 1990's it rose to around 2 msec.
    Now, it is around 1 msec.

    Here is a plot

    http://www.iers.org/MainDisp.csl?pid=95-100

    Only the long period variations count for leap seconds - the seasonal
    and other high frequency
    oscillations tend to average out.

    In the early part of the last century (~1905), it decreased by ~ 5
    msec in a year or so.
    If that happened right now, it would go to ~ -4 msec negative, and we
    would be seeing
    2 negative leap seconds or more per year. Even if the decrease from
    1975 to 1985 happened again, it
    would be at -1 msec, and we would have a negative leap second every
    two years or so.

    What is a reasonable assumption is that we would likely have a year or
    more warning of the
    likelihood of a negative leap second.

    Regards
    Marshall Eubanks

    >
    >
    > Warner
    > _______________________________________________
    > ntpwg mailing list
    > ntpwg@lists.ntp.org
    > https://lists.ntp.org/mailman/listinfo/ntpwg



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