[LEAPSECS] My FOSDEM slides

[Brooks Harris]

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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