[LEAPSECS] BBC radio Crowd Science

[michael.deckers]

    On 2017-01-29 16:18, John Sauter wrote:



> Based on the definition of UTC, it seems to me that there are two
> cases, both of which are very simple.  For a negative leap second, the
> change in TAI - UTC happens instantly at UTC midnight, which is one
> second after 23:59:58, when the difference changes by -1.  For a
> positive leap second, the change happens gradually over the time of the
> leap second, from 23:59:60 to midnight, when the difference slowly
> changes by +1.

    No, the difference TAI - UTC cannot change "slowly" because
    it always must be an integral number of seconds. ITU-R TF.460-6
    says
       "It [UTC] corresponds exactly in rate with TAI but differs
       from it by an integer number of seconds."
    Changing the difference "slowly" in the sense of differentiable
    would also cause a deviation in rate between TAI and UTC.


> This sounds like an interesting story--can you provide more details, or
> a reference?  I was able to learn only the basic facts:
>
> http://www.bipm.org/metrology/ionizing-radiation/units.html

    The SI deviates from two of their principles with the
    introduction of the unit Sv: having at most one derived
    SI unit per dimension ("kind of quantity"), and not using
    the unit to specify the quantity. The excuses are in the
    "Considering" sections of CGPM 16 1979, Resolution 5 and
    CIPM Recommendation 1 of 1984, as reprinted in the SI Brochure
    [http://www.bipm.org/utils/common/pdf/si_brochure_8.pdf].

    Michael Deckers.


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