[LEAPSECS] Common Calendar Time (CCT) -Brooks Harris

[Zefram]

Brooks Harris wrote:

>The best I'd thought of so far was "Proleptic TAI" and "Proleptic

>UTC", but I agree those concepts along that portion of the timescale

>may want their own names.


If those columns of the table refer to your proleptic extensions of
these time scales, then in principle it's valid to use them for such
early times.  The columns do then need to be labelled accordingly; it
is not correct to confuse your extensions with the existing time scales
themselves.  However, before you can use your extended time scales in this
way you need to define them, which you have not done.  You've expressed an
intention for your time scales to behave as proleptic extensions of the
modern time scales, but this does not imply enough detail to use them.
Your table also implies the relationship between the two (proTAI -
proUTC = 10 s prior to 1972), but that's also not enough detail, and
that relationship conflicts with the "proleptic UTC" concept.


>The point, as explained in earlier, email is to intentionally sweep

>the history under the rug prior to 1972-01-01T00:00:00Z.


Sweeping history under the rug doesn't solve anything.  If you're
concerned about precise timing of pre-1972 events then you need to
address the time scales and technology that actually apply to that era.
For the specific context of understanding the NTP and POSIX epochs,
their purely formal use of timestamps such as "1900-01-01 00:00:00 UTC"
is a case where the history of UTC *is* successfully ignored, by virtue
of not counting actual seconds and not processing timestamps early enough
to matter.  For example, the NTPv4 spec, RFC 5905, says

    In the date and timestamp formats, the prime epoch, or base date of
    era 0, is 0 h 1 January 1900 UTC, when all bits are zero.  It should
    be noted that strictly speaking, UTC did not exist prior to 1 January
    1972, but it is convenient to assume it has existed for all eternity,
    even if all knowledge of historic leap seconds has been lost.

I'm not sure what's left that you think you're adding to pre-1972 time
scales.  You're not creating a time scale that can be used to describe
actual precise pre-1972 instants.  It seems that your idea of CCT is
a purely notional proleptic extension of UTC, but that's what NTP (and
arguably POSIX) already uses without difficulty.


>NTP clearly has 10 Leap Seconds in effect at its "1900" "prime epoch"

>on the "Proleptic UTC" timescale.


Where do you get that idea?  NTP doesn't represent the TAI-UTC difference
anywhere, and increases time values by 86400 per UTC day regardless
of leaps.  The NTPv4 definition that I quoted above is even explicit in
saying that pre-1972 leap history is unknown in its notional proleptic
UTC.

-zefram