FW: Time Zone change for San Luis, Argentina

Olson, Arthur David (NIH/NCI) [E] olsona at dc37a.nci.nih.gov
Mon Mar 16 19:19:55 UTC 2009

I'm forwarding this message from NorbertoNazabal, who is not on the time zone mailing list. Those of you who are on the list, please direct replies appropriately.


From: Norberto Nazabal [mailto:nazabal at gmail.com] 
Sent: Monday, March 16, 2009 3:19
To: Jesper Nørgaard
Cc: TZ-list
Subject: Re: Time Zone change for San Luis, Argentina

Hi Jesper,

Thanks for you answer, I want to let you know that currently we are using the GMT-4 time zone here at San Luis, since the last Sunday 15th at 00:00.
I checked the Chile DST and I think we will use the same time zone, but I will try to contact to somebody in the goverment to confirm that information.
Thanks for your notes about the consistency issues and I hope the new time zone for San Luis can be added to your database after the confirmation of which time zone we will use.


Norberto Nazabal.

2009/3/16 Jesper Nørgaard <jnorgard at prodigy.net.mx>
Norberto Nazabal wrote:
>Basically the law says:
>1) We will use the time zone GMT-3 from the 0 hour of the second Sunday of October to the 24 hours of the second Saturday of April.
>2) We will use the time zone GMT-4 from the 0 hour of the second Sunday of April to the 24 hours of the second Saturday of October.
I agree that this is an accurate translation of the document which was published already back in December 2008. However this definition contains serious problems of consistency. And not only that, if this was published so long back (2-3 months) why was it not followed in 2009, but rather following the Chile DST and Buenos Aires Argentinian DST instead with a frantic press conference the Thursday before the weekend when it was implemented?
The problem of consistency is the perhaps not obvious fact that the Second Saturday of a month at 24:00 is *not* always the same time as the Second Sunday at 0:00 of a month. Thus the above definition is not always defining two contiguous periods (DST and non-DST) as one might think. I am sure this is an attempt to give an intuitive definition where one period goes to the 24:00 hours of one day, and is replaced with a new period starting at 0:00 hour the next day, but it fails. The first problem will occur in 2012 where the Second Saturday is 14.th. of April while the Second Sunday is the 8.th. of April (e.g. the problem occurs when the first in the month is a Sunday). So literally the definition will have it that GMT-3 will be followed from 2011-10-09 00:00:00 to 2012-04-14 24:00:00 and GMT-4 will be followed from 2012-04-08 00:00:00 : During a week we have both GMT-3 and GMT-4 ??
The most probable scenarios are that either San Luis redefines the decree in a consistent way, or that either Chile DST or Argentina DST is followed. The future will tell. Already in October 2009 the two latter are different, Chile starts DST 2009-10-11 00:00:00 and Buenos Aires starts DST 2009-10-18 00:00:00.
Regards, Jesper Nørgaard Welen

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