[LEAPSECS] Leap seconds have a larger context than POSIX

[Michael Deckers]

    On 2020-02-04 21:16, Steve Allen wrote:


> The first time that the 4th meeting of the CCDS happened was in 1966,
> but that meeting is not found in any official record.  The meeting
> ended with a vote to recommend that the CGPM should adopt an SI second
> based on cesium, but the circumstances of that vote were deemed so
> abusive that the entire meeting was nullified.  That did not stop the
> rush for an atomic second.  During the next year subsets of the CCDS
> members gathered for discussions at other meetings.  When the second
> 4th meeting of the CCDS was held in 1967 they did recommend the cesium
> second to the CGPM.


    From the standpoint of a physicist, the 1960 definition of the SI second
    (based on ET and Newcomb's tables for the Sun) was extremely 
impractical.
    With the wide availability of Cs clocks, the atomic second was much
    easier and more precisely reproducible than the SI second, so a
    redefinition of the second (or at least a practical unit, as with
    the recently abolished practical volt and ohm) was urgent.

    On the other hand, you are certainly right that the actions of the
    CCDS in 1967 appear strange: they propose to redefine the SI second,
    and then go on to propose that the BIH, IAU, IUGG, URSI, and CCIR
    study the problems arising from the new definition ("étudier les
    problèmes soulevés par l'application des décisions prises
    concernants la nouvelle définition de l'unité du temps").
    Apparently, it did not even occur to them that this is bad
    engineering.

    The proposal of the IAU GA13 in 1967 to introduce an (unsteered)
    international atomic time scale would have allowed to study the
    possible problems of a redefinition of the SI second before
    applying it.



> Folks at the PTB took a different aim by introducing draft legislation
> that the German government passed in 1969.  The law made it illegal
> for the German government to broadcast anything other than SI seconds,
> and it would become effective in 1970.  This seems to have pulled the
> trigger on the CCIR process, for without some kind of quick action a
> major nation would be broadcasting time signals using a different
> scale than other nations.

    The law on legal units in West Germany, from 1969-07-02, lists under
    the title "tasks of the Physikalisch-Technische Bundesanstalt"
    that the PTB has to publicize the procedures by which units without
    material prototype are realized, including the units of time and
    time scales, as well as the temperature unit and temperature scales.
      (" hat die Verfahren bekanntzumachen, nach denen nicht verkörperte
         Einheiten, einschließlich der Zeiteinheiten und der Zeitskalen
         sowie der Temperatureinheit und Temperaturskalen, dargestellt
         werden,")
    This can be taken to imply the task to disseminate a standard
    frequency (which they already did). But in my opinion it does not
    imply that UTC must have the same rate as the atomic time scales
    at the time -- the law even allows for several time scales.

    I'll try to find out how the PTB was involved in this legislation
    as far as time in concerned. In Germany, federal law can only
    be proposed by members of parliament, and by federal and state
    governments; but the PTB was certainly heard during the legislative
    process.



> In my home state of California the process that led to UTC with leap
> seconds would have been illegal under the Brown Act that requires
> public access to meetings.  But in the full context that is not the
> most criminal aspect of the process that led to the 1970 CCIR
> decision.


    Yes, and the ITU-R deliberations before the WRC in 2015 were not
    transparent either. Nevertheless, past decisions of the CCIR and
    the IAU have become accessible nowadays.

    Let's hope that the CIPM treats any future discussions about
    a redefinition of UTC in an open manner, and that it adheres
    to rational design and decision processes. The recent revision
    of the SI has been largely transparent and guided by good practices.

    Michael Deckers.