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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