Leap second functional question - NTP

This is a discussion on Leap second functional question - NTP ; Hello Bill, On Friday, February 22, 2008 at 1:29:07 +0000, Unruh wrote: > there have been no leap seconds for the past 4 years or so There was a leap a little over 2 years ago, on 31 December 2005 ...

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Thread: Leap second functional question

  1. Re: Leap second functional question

    Hello Bill,

    On Friday, February 22, 2008 at 1:29:07 +0000, Unruh wrote:

    > there have been no leap seconds for the past 4 years or so


    There was a leap a little over 2 years ago, on 31 December 2005 23:59:60
    It's already decided that there will be no leap in next June, so the
    next open date is 31 December 2008. But DUT1 reached -0.4 seconds only
    very recently, so maybe not yet... I'd bet on June 2009, when DUT1 will
    be around -0.8 ;-)


    Serge.
    --
    Serge point Bets arobase laposte point net

  2. Re: Leap second functional question

    Bill,

    Before 1972 there were no leap secconds; however there were periodic
    introductions of tiny rate adjustments relative to Ephemeris Time (ET)
    that drove everybody nuts. There never has been and most likely never
    will be leap deletions. In any case the timecode generators at WWVB and
    WWV cannot handle deletions.

    There seems to be widespread misinterpretation on how NTP handles leap
    seconds. Please see: http://www.eecis.udel.edu/~mills/leap.html.

    The historical and technical basis for the chronometry and metrology of
    the NTP timescale has been carefully considered and published:
    http://www.eecis.udel.edu/~mills/dat...apers/time.pdf. This includes
    the historic introduction of ET, TAI, UTC and leap seconds. There have
    been some attempts to project the Earth wobble into the future, but the
    only reliable predictions now come from the IERS. The historic record of
    the NTP project, inlcuding the adoption of the NTP timescale, has been
    published: http://www.eecis.udel.edu/~mills/dat...rs/history.pdf.

    Dave

    Unruh wrote:
    > David Woolley writes:
    >
    >
    >
    >>>You are asking for the impossible! Leap seconds keep time in synch with

    >
    >
    >>That was the intention. I was pointing out that you can only use "true"
    >>time to represent historic civil times, you cannot calculate the "true"
    >>time of a future civil time beyond the first candidate leap second.

    >
    >
    >
    >>>the earth's rotation. The rate of rotation is subject to small
    >>>variations. This is why leap seconds occur at irregular intervals and
    >>>why it is possible to have a negative leap second, although I don't
    >>>recall that we ever had one.
    >>>

    >>
    >>Exactly, which is why the question casts doubt on the use of "true"
    >>time, which was my intention.

    >
    >
    > Well, I suppose one could assume no leap seconds into the future. It is as
    > good as UTC which does exactly that, except it also assumes no leap seconds
    > into the past, where we know it is wrong. Getting it half right would seem
    > an advance.
    >


  3. Re: Leap second functional question

    On Feb 22, 10:51 am, "David L. Mills" wrote:
    > Before 1972 there were no leap secconds; however there were periodic
    > introductions of tiny rate adjustments relative to Ephemeris Time (ET)
    > that drove everybody nuts.


    The broadcast time signals in the 1960s were so confusing that NASA
    employed a geodesist to produce an explanation of how to interpret
    them. He interviewed USNO's Markowitz, the chairman of IAU Comm 31
    (Time) who was a principal in adapting cesium resonators to the scheme
    of broadcast time. The writeup is online at
    http://ntrs.nasa.gov/archive/nasa/ca...1966020453.pdf
    The report uses terminology about time scales which was new and
    evolving even at the time, and which has since been discarded, but
    because it was produced for an audience other than those who ran the
    time service bureaus it does define the terms pretty well -- well
    enough to make it clear what a nightmare the pre-leap second scheme
    was.

  4. Re: Leap second functional question

    sla29970,

    I stand corrected; it was the CCIR, not the CCITT. This is because the
    ITU recommendations are specifically for standard time and frequency
    dissemination by, for example, WWV/B/H and their international counterparts.

    My reference for leap second introduction was CCIR Recommendation 517,
    which permits leaps only June/December. However, I just dug up the most
    recent ITU-R Proposed Recommendation TF.460-6 (2007)
    http://www.fcc.gov/ib/sand/irb/werit...1893wp7a/1.doc, which says
    first preference is June/December, second preference is March/September
    and that standard time will continue in UTC with DUT1 and leap seconds.

    I hope this is the end of it, but I bet it's not.

    Dave

    sla29970@gmail.com wrote:

    > On Feb 21, 3:15 pm, "David L. Mills" wrote:
    >
    >>The current
    >>code here can leap at the end of any month, which seems to be the
    >>prevailing view of the standards folks. However, I can't find
    >>confirmation at the IERS site.

    >
    >
    > Images of the IAU proceedings from the General Assembly in 1973 are at
    > http://www.ucolick.org/~sla/leapsecs...oc1973p154.gif
    > http://www.ucolick.org/~sla/leapsecs...oc1973p155.gif
    > This was the assembly immediately after leap seconds began (and the
    > first one at which the IAU could make any response, given that the
    > CCIR neglected to send them a letter in 1970 leaving them no standing
    > upon which to comment on leap seconds before they began). The changes
    > recommended by the IAU in 1973 were incorporated into the first
    > revision of what is now known as ITU-R TF.460, notably, that it was
    > foreseeable that leap seconds would be needed more than twice a year.


  5. Re: Leap second functional question

    On Feb 22, 12:26 pm, "David L. Mills" wrote:
    > My reference for leap second introduction was CCIR Recommendation 517,
    > which permits leaps only June/December.


    For reference, that is now known as ITU-R RA.517, available for
    purchase at
    http://www.itu.int/rec/R-REC-RA.517/en
    as near as I can tell, any language on leap seconds was merely by
    reference to what is now known as ITU-R TF.460, and it had all been
    removed prior to revision 3 of that document which is now at revision
    4.

    Sigh. When its name was CCIR it was dismayingly poor at
    consultation. Now that its name is ITU-R it is still dismayingly poor
    at communication. I don't like it when international standards needed
    by lots of operational systems are hidden away in proprietary
    documents.

  6. Re: Leap second functional question

    sla29970@gmail.com wrote:
    > On Feb 22, 12:26 pm, "David L. Mills" wrote:
    >
    >>My reference for leap second introduction was CCIR Recommendation 517,
    >>which permits leaps only June/December.

    >
    >
    > For reference, that is now known as ITU-R RA.517, available for
    > purchase at
    > http://www.itu.int/rec/R-REC-RA.517/en
    > as near as I can tell, any language on leap seconds was merely by
    > reference to what is now known as ITU-R TF.460, and it had all been
    > removed prior to revision 3 of that document which is now at revision
    > 4.
    >
    > Sigh. When its name was CCIR it was dismayingly poor at
    > consultation. Now that its name is ITU-R it is still dismayingly poor
    > at communication. I don't like it when international standards needed
    > by lots of operational systems are hidden away in proprietary
    > documents.


    Who pays the people who develop the standards?? For their time? Their
    travel to attend meetings? Sometimes their employers will fund this
    sort of thing but if it's not business related they have no obligation
    to do so.


  7. Re: Leap second functional question

    David Woolley wrote:
    > Evandro Menezes wrote:
    >
    >> Aren't you confusing UTC and GMT? Or maybe I'm the one confusing
    >> both...

    >
    > Nearly everyone confuses UTC and GMT. GMT is an obsolete name for UT1,
    > or something close, but the BBC still uses it to, incorrectly, mean UTC.


    That's actually not true. GMT exists in the UK as the local time zone
    reference name. GMT was renamed UTC for mostly political reasons. GMT
    follows UTC but it isn't an incorrect reference.

    Danny

  8. Re: Leap second functional question

    > Date: Fri, 22 Feb 2008 17:55:04 -0500
    > From: Danny Mayer
    > Sender: questions-bounces+oberman=es.net@lists.ntp.org
    >
    >
    > David Woolley wrote:
    > > Evandro Menezes wrote:
    > >
    > >> Aren't you confusing UTC and GMT? Or maybe I'm the one confusing
    > >> both...

    > >
    > > Nearly everyone confuses UTC and GMT. GMT is an obsolete name for UT1,
    > > or something close, but the BBC still uses it to, incorrectly, mean UTC.

    >
    > That's actually not true. GMT exists in the UK as the local time zone
    > reference name. GMT was renamed UTC for mostly political reasons. GMT
    > follows UTC but it isn't an incorrect reference.


    Are you really sure? I've always read that GMT is UT1, not UTC. I just
    read the article on wikipedia and it seems to agree that GMT is UT1.

    Of course, UT1 is always within 1 second of UTC.

    In any case, the definitions in the various Wikipedia articles (UTC, UT,
    and GMT) all agree with what I learned dealing with timing issues in the
    past, although both those folks (the ones in Boulder, Colorado) and
    Wikipedia could be wrong.

    The article also states that UTC does not always have 86,400 seconds in a
    day, although POSIX specifies that a day is always 86,400 seconds long.

    If anyone can provide a reference from one of the real standards
    specifications, I would appreciate it. (If it does not match with the
    information I have received form the NIST folks in Boulder, I'll be very
    surprised.)
    --
    R. Kevin Oberman, Network Engineer
    Energy Sciences Network (ESnet)
    Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
    E-mail: oberman@es.net Phone: +1 510 486-8634
    Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751

  9. Re: Leap second functional question

    On Feb 22, 4:02 pm, ober...@es.net (Kevin Oberman) wrote:
    > Are you really sure? I've always read that GMT is UT1, not UTC. I just
    > read the article on wikipedia and it seems to agree that GMT is UT1.


    Please have a look at
    http://ntrs.nasa.gov/archive/nasa/ca...1966020453.pdf
    That's 207 pages of document basically explaining that during the
    1960s the nomenclature was chaotic. The US NBS station WWV/WWVB were
    broadcasting what is now known as the old form of UTC, which attempted
    to track UT2 (not UT1), and calling it GMT, but the time bureaus
    themselves had a whole other vocabulary. Given the history it is not
    productive to press this sort of argument.

  10. Re: Leap second functional question

    Kevin Oberman wrote:
    >> Date: Fri, 22 Feb 2008 17:55:04 -0500
    >> From: Danny Mayer
    >> Sender: questions-bounces+oberman=es.net@lists.ntp.org
    >>
    >>
    >> David Woolley wrote:
    >>> Evandro Menezes wrote:
    >>>
    >>>> Aren't you confusing UTC and GMT? Or maybe I'm the one confusing
    >>>> both...
    >>> Nearly everyone confuses UTC and GMT. GMT is an obsolete name for UT1,
    >>> or something close, but the BBC still uses it to, incorrectly, mean UTC.

    >> That's actually not true. GMT exists in the UK as the local time zone
    >> reference name. GMT was renamed UTC for mostly political reasons. GMT
    >> follows UTC but it isn't an incorrect reference.

    >
    > Are you really sure? I've always read that GMT is UT1, not UTC. I just
    > read the article on wikipedia and it seems to agree that GMT is UT1.
    >


    The official standards body for this in the UK is the National Physics
    Laboratory so that's where you should look. The general reference is
    here: http://www.npl.co.uk/server.php?show=nav.275 Specifically you
    should look at the following PDF:
    http://www.npl.co.uk/upload/pdf/Timescales_ADDED.pdf which specifies
    that "GMT remains the legal basis of the civil time for the UK." and
    "adopted the term Universal Time (UT) for the "new" GMT." Interesting
    enough it says UT and not UTC or UT1. The next paragraph talks about the
    UT% types and how UT1 is the only one in widespread use but does not say
    that GMT uses it.

    The following document does say that GMT is UT1:
    http://www.npl.co.uk/upload/pdf/The_...nd_PENDING.pdf
    "In effect, the length of the seconds of Universal Time (UT1, as GMT is
    now officially known) varies slightly to keep in step with the changes
    in the Earth's rotation."

    I do know that the BBC inserts a leap second when needed (I've heard
    them to it - an extra long pip within the regular 6 pips.

    I stand corrected.

    Danny
    > Of course, UT1 is always within 1 second of UTC.
    >
    > In any case, the definitions in the various Wikipedia articles (UTC, UT,
    > and GMT) all agree with what I learned dealing with timing issues in the
    > past, although both those folks (the ones in Boulder, Colorado) and
    > Wikipedia could be wrong.
    >
    > The article also states that UTC does not always have 86,400 seconds in a
    > day, although POSIX specifies that a day is always 86,400 seconds long.
    >
    > If anyone can provide a reference from one of the real standards
    > specifications, I would appreciate it. (If it does not match with the
    > information I have received form the NIST folks in Boulder, I'll be very
    > surprised.)


    See above for the UK.

    Danny

  11. Re: Leap second functional question

    sla29970,

    Thanks for the report, which has personal nostalgia for me. My logbook
    has all US Navy loudenboomers on all frequencies including VLF. WWVL on
    20 kH haa long been a silent key. The LORAN 1-PPS pulses alledged from
    Cape Fear never came from there; they came, as I personally verified,
    from Coast Guard NAVCEN in Wildwood, NJ. NASA should have had more
    influence on WWV, as the original location of the WWV transmitters was
    at what is now NASA Goddard (GSFS) in Greenbelt, MD. I once lived about
    a mile from there. The original quartz oscillators were and so far as I
    know are still buried in holes twenty feet deep. The NASA Goddard ham
    radio station W3NAN occupies the site.

    There are many minor technical errors in the report, but it is still
    fun reading. The author missed Navy NST/AOK... station once known from
    Aorta, Spain. For whatever reason, there is no mention whatsoever of the
    US Navy Omega VLF system, once the worldwide timing beacon before
    satellite. I know that since I have one of the original Cesium
    oscillators once used to calibrate the eight stations. It was
    transported all over the world as an international first-class air
    passenger complete with battery case. I have its logbook.

    Dave

    sla29970@gmail.com wrote:
    > On Feb 22, 10:51 am, "David L. Mills" wrote:
    >
    >>Before 1972 there were no leap secconds; however there were periodic
    >>introductions of tiny rate adjustments relative to Ephemeris Time (ET)
    >>that drove everybody nuts.

    >
    >
    > The broadcast time signals in the 1960s were so confusing that NASA
    > employed a geodesist to produce an explanation of how to interpret
    > them. He interviewed USNO's Markowitz, the chairman of IAU Comm 31
    > (Time) who was a principal in adapting cesium resonators to the scheme
    > of broadcast time. The writeup is online at
    > http://ntrs.nasa.gov/archive/nasa/ca...1966020453.pdf
    > The report uses terminology about time scales which was new and
    > evolving even at the time, and which has since been discarded, but
    > because it was produced for an audience other than those who ran the
    > time service bureaus it does define the terms pretty well -- well
    > enough to make it clear what a nightmare the pre-leap second scheme
    > was.


  12. Re: Leap second functional question

    sla29970,

    Yes, I found the same brick wall. Fortunately, the FCC said up-yours to
    the ITU and published the latest draft complete with blue-lined new text
    and red-lined deleted text. I have some CCIR documents from long ago and
    they cost a king's ransom in Swiss francs.

    Dave

    sla29970@gmail.com wrote:

    > On Feb 22, 12:26 pm, "David L. Mills" wrote:
    >
    >>My reference for leap second introduction was CCIR Recommendation 517,
    >>which permits leaps only June/December.

    >
    >
    > For reference, that is now known as ITU-R RA.517, available for
    > purchase at
    > http://www.itu.int/rec/R-REC-RA.517/en
    > as near as I can tell, any language on leap seconds was merely by
    > reference to what is now known as ITU-R TF.460, and it had all been
    > removed prior to revision 3 of that document which is now at revision
    > 4.
    >
    > Sigh. When its name was CCIR it was dismayingly poor at
    > consultation. Now that its name is ITU-R it is still dismayingly poor
    > at communication. I don't like it when international standards needed
    > by lots of operational systems are hidden away in proprietary
    > documents.


  13. Re: Leap second functional question

    Richard,

    There might actually have been standards committee members paid by the
    ITU, but I never met one. They were all paid by private and sometimes
    government sources who had very real private agendae. Sometimes when the
    discussions got hot the expert smokejumpers were parachuted in from
    corporate headquarters. One of them was me and I waS paid as a DARPA
    contractor.

    Dave

    Richard B. Gilbert wrote:

    > sla29970@gmail.com wrote:
    >
    >> On Feb 22, 12:26 pm, "David L. Mills" wrote:
    >>
    >>> My reference for leap second introduction was CCIR Recommendation 517,
    >>> which permits leaps only June/December.

    >>
    >>
    >>
    >> For reference, that is now known as ITU-R RA.517, available for
    >> purchase at
    >> http://www.itu.int/rec/R-REC-RA.517/en
    >> as near as I can tell, any language on leap seconds was merely by
    >> reference to what is now known as ITU-R TF.460, and it had all been
    >> removed prior to revision 3 of that document which is now at revision
    >> 4.
    >>
    >> Sigh. When its name was CCIR it was dismayingly poor at
    >> consultation. Now that its name is ITU-R it is still dismayingly poor
    >> at communication. I don't like it when international standards needed
    >> by lots of operational systems are hidden away in proprietary
    >> documents.

    >
    >
    > Who pays the people who develop the standards?? For their time? Their
    > travel to attend meetings? Sometimes their employers will fund this
    > sort of thing but if it's not business related they have no obligation
    > to do so.
    >


  14. Re: Leap second functional question

    Unruh wrote:

    > A common misconception. The GPS people actually dynaically track the time
    > delivered by the sattelites and adjust their scales accordingly. Even if
    > they know nothing of GR, they would have discovered that the clocks were
    > running a bit fast and applied a correction fudgefactor. The problem is


    The 1995 GLOBAL POSITIONING SYSTEM STANDARD POSITIONING SERVICE SIGNAL
    SPECIFICATION .
    on page 18, explicitly refers to relativistic corrections:

    < centered about L1. The carrier frequency for the L1 signal is coherently
    derived from a frequency source within the satellite. The nominal
    frequency of this source -- as it appears to an observer on the ground
    -- is 1.023 MHz. To compensate for relativistic effects, the output
    frequency of the satellite's frequency standard -- as it would appear to
    an observer located at the satellite -- is 10.23 MHz offset by a
    ∆f/f = -4.4647 x 10-18 or a ∆f = -4.567 x 10-3 Hz. This frequency offset
    results in an output of 10.22999999543 MHz, which is frequency divided
    to obtain the appropriate carrier modulation signal (1.022999999543
    MHz). The same output frequency source is also used to generate the
    nominal L1 carrier frequency (fo) of 1575.42 MHz.>>

    Also, on page 39, it puts an explicit requirement on receivers to apply
    a relativistic correction. I'm not sure if this is SR, GR, or a mix. I
    think this is referring to relativistic effects along the whole signal
    propagation path.

    < apparent to the control segment two-frequency receivers for the interval
    of time in which the parameters are transmitted. This estimated
    correction accounts for the deterministic satellite clock error
    characteristics of bias, drift and aging, as well as for the satellite
    implementation characteristics of group delay bias and mean differential
    group delay. Since these coefficients do not include corrections for
    relativistic effects, the user's equipment must determine the requisite
    relativistic correction. Accordingly, the offset given below includes a
    term to perform this function.>>

  15. Re: Leap second functional question

    Unruh wrote:
    >>> While it may be slowing on average, it is noise and it could well speed up
    >>> as well.

    >
    >>Noise implies that the changes are both positive and negative, in

    > They are
    >>which case a leap second won't be needed. If it is systematic,

    > They would still be needed. Just because your computer's drift rate is both
    > positive and negative does not mean that compensation is not needed.
    > They do not necessarily average out on the time scale of years.
    >
    > There is a net drift to longer days. but superposed on that is a noise
    > which even over the time scale ofyears makes a difference. An earthquake in
    > Java rearranges the moment of inertia of the earth and changes the rotation
    > rate of the earth, and it can be positive or negative.
    >
    >>i.e. the changes are more in one direction than another, a leap second
    >>will be needed.

    >
    > It is needed even if it equal in both directions over a long time.


    It is needed if the noise is equal in both directions *and* if the
    average is somewhere near zero.

    Besides the noise, there is a strong forward bias as well. The second
    is based on earth rotation in 1900. The past century has allowed for
    the average rate to slow significantly since then.

    So a negative leap will only be needed if the noise is strong enough to
    wipe out the entire bias. The recent speedup has only been strong
    enough to delay the positive second additions, not reverse them.


    (Excess Length of Day plot).


    --
    Darren Dunham ddunham@taos.com
    Senior Technical Consultant TAOS http://www.taos.com/
    Got some Dr Pepper? San Francisco, CA bay area
    < This line left intentionally blank to confuse you. >

  16. Re: Leap second functional question

    On Feb 25, 9:53 am, ddun...@taos.com (Darren Dunham) wrote:
    > The second is based on earth rotation in 1900.


    The SI second is based on the ephemeris second, which is based on the
    earth's mean orbital motion in 1900, but that definition corresponds
    to the mean solar second of earth's rotation from around the year 1820
    or so, and this is not NTP so can it move to an astronomy group?

  17. Re: Leap second functional question

    ddunham@taos.com (Darren Dunham) writes:

    >Unruh wrote:
    >>>> While it may be slowing on average, it is noise and it could well speed up
    >>>> as well.

    >>
    >>>Noise implies that the changes are both positive and negative, in

    >> They are
    >>>which case a leap second won't be needed. If it is systematic,

    >> They would still be needed. Just because your computer's drift rate is both
    >> positive and negative does not mean that compensation is not needed.
    >> They do not necessarily average out on the time scale of years.
    >>
    >> There is a net drift to longer days. but superposed on that is a noise
    >> which even over the time scale ofyears makes a difference. An earthquake in
    >> Java rearranges the moment of inertia of the earth and changes the rotation
    >> rate of the earth, and it can be positive or negative.
    >>
    >>>i.e. the changes are more in one direction than another, a leap second
    >>>will be needed.

    >>
    >> It is needed even if it equal in both directions over a long time.


    >It is needed if the noise is equal in both directions *and* if the
    >average is somewhere near zero.


    >Besides the noise, there is a strong forward bias as well. The second
    >is based on earth rotation in 1900. The past century has allowed for
    >the average rate to slow significantly since then.


    >So a negative leap will only be needed if the noise is strong enough to
    >wipe out the entire bias. The recent speedup has only been strong
    >enough to delay the positive second additions, not reverse them.


    Yes. And? All you would need is twice the recent speedup and you would get
    a decriment. It may not happen, but then again it may.


    >
    > (Excess Length of Day plot).



  18. Re: Leap second functional question

    On Friday, February 22, 2008 at 16:52:17 +0100, Serge Bets wrote:

    > It's already decided that there will be no leap in next June [2008],
    > so the next open date is 31 December 2008. But DUT1 reached
    > -0.4 seconds only very recently, so maybe not yet... I'd bet on
    > June 2009, when DUT1 will be around -0.8 ;-)


    Miserably lost bet! Please remember to never trust this guy again with
    his poor attempts to predict the future. ;-)


    Serge.
    --
    Serge point Bets arobase laposte point net

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