On 2015-03-06 08:30 PM, Paul Hirose wrote:
On 2015-03-06 11:04, Brooks Harris wrote:
The "rubber-band era" is
just entirely irrelevant. Its historically interesting, and may be
required for some special application concerning that period, but for
practical "UTC-like" timekeeping its just an historical curiosity.
This fact is somewhat more apparent looking at the IERS publication
Leap_Second_History.dat, at
https://hpiers.obspm.fr/eoppc/bul/bulc/Leap_Second_History.dat. There we
see *no values* before "1 1 1972" - the "rubber-band era" is gone.
That's correct - the "rubber band era" no long exists.
Since the name of the document is "leap second history", the rate
offsets and fractional second step adjustments before 1972 aren't
applicable. They can be found elsewhere at the IERS site:
http://hpiers.obspm.fr/eop-pc/index.php?index=UTC&lang=en
I distribute a Windows astronomical toolbox DLL which includes time
scale conversions. Since astronomy often requires analysis of old
data, the DLL can deal with pre-1972 UTC. I won't get into the dispute
over whether or not that's bona fide UTC! However, the IERS and USNO
recognize it as such, so I assume the user will expect time
conversions to work in that era. (I have never needed that capability
myself.)
Of course its important the purpose of any timescale be stated
carefully, and I haven't done that in what I wrote in the email
containing this paragraph. In the company of the astronomers here on the
list I might have been a bit insensitive to lump their objectives into
"some special application".
The challenge I'm trying to solve is to provide a deterministic
timekeeping and labeling scheme for date and time *after*
1972-01-01T00:00:00Z (UTC) = 1972-01-01T00:00:10 (TAI). This is
essentially the purpose of "civil time" timekeeping as is typically
intended. The timescale I've attempted to describe is intended to be
single reference timescale with a *fixed epoch* at the NTP prime epoch
era 0. (Conceptually this could be extended into the indefinite past.)
The timescale before 1972 is an abstract proleptic Gregorian calendar
scale for purposes of calculation convenience. On this scale, like NTP,
PTP, and POSIX, any date-time before 1972-01-01T00:00:00Z (UTC) is
considered either inaccurate or invalid.
It is in that sense, and with regard to that purpose, I said "The
"rubber-band era" is just entirely irrelevant.".
-Brooks
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