[LEAPSECS] leapseconds, converting between GPS time (week, second) and UTC

[Steve Allen]

On Tue 2019-01-15T10:50:10-0800 Tom Van Baak hath writ:
> Nope.  All minutes have 60 seconds in Excel.  And in Windows.  And
> in Unix/POSIX.  Really any computer system that uses a fixed "epoch"
> and a ticking "counter" is ruined by leap seconds.  The systems differ
> in their epoch's, they all differ in their counters, they can all be
> set to UTC, except they all fail when there's a positive or negative
> leap second.

Nowhere did the folks who were there at the inception of leap seconds
say so explicitly, but from reading how things worked over the history
of the time services and what the folks paid to provide those services
wrote, I am reasonably sure that they also believed that all minutes
consisted of 60 seconds, and all days consisted of 86400 seconds.

I believe that the concept in their heads was that occasionally there
are two calendar days which are not adjacent by one SI second.  Or, if
the earth rotation were to speed up enough, there might be two
calendar days which overlap by one SI second.  The notation 23:59:60
is merely a tag for conveniently indicating when a second was inserted
between two calendar days.  The clock is disconnected from the calendar.

Understandably this notion should trigger objections that it is
technically barren.  At this point I would answer "Yes, and they knew
that."  They were being paid by their governments to provide the legal
and operational time of their nations.  Their job had always been to
tell the people of their country how to set their clocks.

So when a senator or cabinet official asked "Can you tell me what time
it is?"  they had learned over the course of their careers that the
answer was not to wander off into a long technical discussion about
how sausage was made, but to smile and say "Yes."

Similarly for the 1970 CCIR decision about leap seconds:  when facing a
chamber full of folks at an international assembly that had the power
to dictate how every member nation should set their clocks in the same
way that was consistent with the laws of all those nations, the answer
was to smile and say "Yes, everyone has agreed that this is the best
way to do it."  Their job was not to say that the technical folks who
made that decision had already decided to disregard that in the systems
that they controlled, broadcast navigational signals based on TAI, and
make almanacs based on UT (not UTC).

--
Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
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