[LEAPSECS] BBC radio Crowd Science

[Brooks Harris]

On 2017-01-30 10:12 AM, Steve Allen wrote:
> On Mon 2017-01-30T14:14:10 +0000, Tony Finch hath writ:
>> I think what I was trying to get at (as others have already said in this
>> thread) is that you can use the TAI-UTC delta to translate from UTC to TAI
>> during a leap second, but you need more information to make the inverse
>> translation.
> As mentioned by Arias in that radio show, there are leaps of one hour
> in time that we deal with regularly.  The tz project has tzdata that
> unambiguously represent when the jump occurs, and the tzcode has a
> convention for how to interpret the ambiguous hour.
>
> (One thing tz cannot do is represent the legal specification of the
> changes in Spain a century ago when the time of fall back was given
> by the decree as 25:00:00 on the date in question.  tz encodes
> those as 01:00:00 on the next date.)
Indeed, while we debate the exact subtle meanings of UTC and Leap 
Seconds the potential inaccuracies of UTC implementations are 
overwhelmed by the potential inaccuracies of local time, both in terms 
of magnitude (1 second TAI-UTC v.s (at least) one hour DST) and in terms 
of clarity of standardization (UTC is pretty well defined, while 
specifications of local time is something of the wild west).

It seems to me Tz Database does a great job of describing the meanings 
of local time after 1972, thanks to the diligent and obsessive work by 
its authors and contributors. As far as I can see, it describes local 
time for contemporary timekeeping, albeit with some quirks and 
exceptions. It has become a de facto standard.

Describing local time before 1972 is going to be a challenge. When was 
the Gettysburg Address delivered? Exactly how was local time understood 
at the time and how would it relate to modern timekeeping practice? This 
is an interesting, fascinating, and probably valuable exercise, but if 
we get too tangled up in those considerations we risk diverting 
attention and energy from the more urgent need of arriving at a uniform 
treatment of local time in contemporary timekeeping systems.

Time Zone Database has become a de facto standard, and IANA's 
involvement has lent it further credibility. But:
A) its only a de facto standard - a due-process standardization process 
is required to achieve world-wide adoption
B) its documentation could be improved because it is complex and quirky
C) its data relies on the reports and judgements of contributors and 
there is no formal process for registering changes
D) its c implementation code is dated and relies on POSIX-time type 
functions and heritage which complicates incorporating Leap Seconds

This is not in anyway a criticism of the years of development in Tz 
Database - its really a fantastic piece of work, hats off.  I only wish 
and hope it will be improved.

-Brooks

>
> --
> Steve Allen                    <sla at ucolick.org>              WGS-84 (GPS)
> UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
> 1156 High Street               Voice: +1 831 459 3046         Lng -122.06015
> Santa Cruz, CA 95064           http://www.ucolick.org/~sla/   Hgt +250 m
> _______________________________________________
> LEAPSECS mailing list
> LEAPSECS at leapsecond.com
> https://pairlist6.pair.net/mailman/listinfo/leapsecs
>
>