Upcoming Indiana time zone moves

Jesper Norgaard Welen jnorgard at prodigy.net.mx
Mon Jan 30 06:01:59 UTC 2006

I think that the tz database should be containing rules that clearly
state which tz transitions will happen, and we should not rely on zic to
"mend things". One of the reasons is not to put an extra burden on
different applications that read the tz database, and another is to
allow people like Deborah Goldsmith and myself to read the rules and
actually understand what goes on.

If we don't need the "CDT" between 2:00 and 3:00 for the good citizens
of Zone Hypothetical, we can just use (1)

Zone Hypothetical       -5:00   -       EST     2006 Apr  2 3:00
                        -6:00   US      C%sT

My argument is that these citizens should not go on Central Daylight
time before the rest of the world, so they will be on EST until 3:00.
However, if we *insist* on having them go on CDT at 2:00 (I still think
that this is an overinterpretation of the DOT ruling, but for arguments
sake), then we should be able to implement it as (2)

Zone Hypothetical       -5:00   -       EST     2006 Apr  2 2:00
                        -6:00   1:00    CDT     2006 Apr  2 3:00
                        -6:00   US      C%sT

Since I don't have zdump here I can't test this, but it works in my
program and my brain. If zic is messing something up here, then I think
zic should be changed, because the input is clear (I hope).

If (1) is acceptable, we are still avoiding the issue a bit, because the
original zone could have used daylight saving too, as an example

Zone Hypothetical       -5:00   US      E%st    2006 Apr  2 2:00
                        -6:00   US      C%sT

this won't work unless zic smoothens out the one hour jumps at 1:59:59
EST to 1:00:00 CST and at 1:59:59 CST to 3:00:00 CDT, so if we want it
to be explicit, to avoid depending on zic, it should be (3)

Zone Hypothetical       -5:00   US      E%st    2006 Apr  2 2:00
                        -6:00   1:00    CDT     2006 Apr  2 3:00
                        -6:00   US      C%sT

Although the above could not be expressed in 2 lines only, it has a
certain elegance because it states "clearly" that something abnormal is
going on between 2:00 and 3:00. 

If we don't let the citizens of Zone Hypothetical go on CDT before the
rest of the world, we would still need 3 lines this way (4)

Zone Hypothetical       -5:00   US      E%st    2006 Apr  2 2:00
                        -5:00   -       EST     2006 Apr  2 3:00
                        -6:00   US      C%sT

I think this a cleaner approach, (3) or (4), than relying on zic to mend
the one-hour hickups. It would impose the need for a complete revision
of the tz database to explicitly express these transitions. 

I would volunteer to find the above fixes to the tz database if there is
nobody else that would. When that is in place, we can revert the changes
to zic that happened in 1996. 

Can anybody test (2) on zdump and report it here?

Any comments are welcome.

Jesper Nørgaard Welen

-----Original Message-----
From: Paul Eggert [mailto:eggert at cs.ucla.edu] 
Sent: Tuesday, January 24, 2006 18:03
To: tz at lecserver.nci.nih.gov
Subject: Re: Upcoming Indiana time zone moves

Arthur David Olson <olsona at elsie.nci.nih.gov> writes:

> + If you want two separate transitions
> + (for example,
> + a one-hour retreat from
> + U. S. Eastern Standard Time
> + to
> + U. S. Central Standard Time
> + followed one hour later by a one-hour advance to
> + U. S. Central Daylight Time),
> + you can artificially
> + (and slightly inaccurately)
> + specify the UTC offset change as occuring a single second too early.

I found that you can do it without the one-second glitch, by coding the
transitions by hand, as follows.

Zone Hypothetical       -5:00   -       EST     2006 Apr  2 7:00u
                        -6:00   -       CST     2006 Apr  2 8:00u
                        -6:00   1:00    CDT     2006 Apr  2 9:00u
                        -6:00   US      C%sT

I couldn't figure out any way to do it with just two transitions, which
would be the obvious way to do it.  (Nor could I do it with wall clock
time; I had to resort to UTC.)

Admittedly this is kind of kludgy.  I suppose zic could make it easier
to shoot yourself in the foot, though surely this is low priority.

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