FW: "Etc\GMT" positive and negative

EXIS.Diaz Lopez, Rodrigo EXIS.rdiaz at iberia.es
Fri Feb 4 09:49:20 UTC 2011


There is an international standard for representation of dates and times: ISO 8601 (see  http://dotat.at/tmp/ISO_8601-2004_E.pdf).

According to ISO 8601, "the representation of the difference (between local time and UTC) can be expressed in hours and minutes, or hours only. It shall be expressed as positive (i.e. with the leading plus sign [+]) if the local time is ahead of or equal to UTC... and as negative (i.e. with the leading minus sign [-]) if it is behind UTC."

And, also according to ISO 86001, ahead of UTC means east of Greenwich and behind UTC means west of Greenwich. For instance, standard offset for Geneva, Switzerland (one hour ahead of UTC) is +01 or +01:00 and standard offset for New York, USA (five hours behind UTC) is -05:00 or -05.

I know, according with this standard, all time zones names in America would be "negative"... but blame it on the International Organization for Standardization.

Best regards.
Rodrigo Díaz López

-----Mensaje original-----
De: Alain Petit [mailto:alain.petit at oracle.com]
Enviado el: jueves, 03 de febrero de 2011 21:03
Para: tz at elsie.nci.nih.gov; tz at lecserver.nci.nih.gov
CC: EXIS.Diaz Lopez, Rodrigo
Asunto: RE: FW: "Etc\GMT" positive and negative


I found the following in the 'etcetera' file.
This seems to explain why your 'positive' zone translate to a 'negative' offset.

# We use POSIX-style signs in the Zone names and the output abbreviations,
# even though this is the opposite of what many people expect.
# POSIX has positive signs west of Greenwich, but many people expect
# positive signs east of Greenwich.  For example, TZ='Etc/GMT+4' uses
# the abbreviation "GMT+4" and corresponds to 4 hours behind UTC
# (i.e. west of Greenwich) even though many people would expect it to
# mean 4 hours ahead of UTC (i.e. east of Greenwich).


-----Original Message-----
From: Ian Abbott [mailto:abbotti at mev.co.uk]
Sent: Wednesday, February 02, 2011 7:42 PM
To: tz at lecserver.nci.nih.gov
Cc: exis.rdiaz at iberia.es
Subject: Re: FW: "Etc\GMT" positive and negative

> From: EXIS.Diaz Lopez, Rodrigo [mailto:EXIS.rdiaz at iberia.es] Sent:
> Tuesday, February 01, 2011 12:25 To: tz at elsie.nci.nih.gov Subject:
> "Etc\GMT" positive and negative
> Hi:
> I think I found a bug with the "Etc\GMT" zones.
> If you use a "positive zone" like Etc\GMT+2 for calculate actual
> local time in this zone you obtain. local time for Etc\GMT-2 (¡a
> negative zone!). For instance, its' 5:00 PM (UTC/GMT), so in GMT+2
> zone (Greece) the local time must be 7:00 PM. But, if you use TZ
> Database, you obtain. ¡3:00 PM!
> And the opposite for "negative zones".
> Is a bit funny. Please, check it.
> I found a web page
> (http://www.gsp.com/support/virtual/admin/unix/tz/gmt/) that use tz
> database (I think) and shows this error.
> Best regards.
> P.S.: It is possible that the problem was with the "codes", because
> in the world there are "GMT+13" and "GMT+14" zones, and these zones
> do not exist in tz database. However, in tz database exists "GMT-13"
> and "GMT-14" zones, that not exist in the real world.

Perhaps this is related to the historical "America not wanting to be
negative" problem that gives us "EST5" being the same as "-0500" in
RFC822 terms?

-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti at mev.co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-

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