[TZInfo-users] GMT timezones

Mark Pentland mark.pent at gmail.com
Mon Dec 20 18:32:32 EST 2010

Hi Phil,

Thanks for the quick reply.

I also suggest using the geographical zones to my users... it was a user of
my system that raised this as a bug....

What confused me further was the site:

It states that Queensland is in GMT+10 ..

http://www.worldtimezone.com/ also shows Brisbane in GMT+10

I'm guessing these sites are not using the POSIX standard...

I think the best solution is to remove the Etc/* timezones from the list on
my site.

Thanks for your help


On Tue, Dec 21, 2010 at 12:16 AM, Philip Ross <phil.ross at gmail.com> wrote:

> Hi Mark,
> On 20 December 2010 02:52, Mark Pentland <mark.pent at gmail.com> wrote:
> > In not sure if i'm missing something but it appears the GMT +- timezones
> are
> > inverted.
> This is the correct behaviour. TZInfo uses data from the tz database
> (http://www.twinsun.com/tz/tz-link.htm), which defines the Etc/GMT+-x
> zones in a POSIX-compliant (and confusing) manner. The documentation
> for the tz database Etc zones states the following:
> # 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).
> > I'm in Brisbane/Australia (GMT + 10), so i'm expecting it to behave
> similar
> > to Etc/GMT+10
> > Is my assumption incorrect?
> Following the POSIX definition, Etc/GMT+10 is a timezone that is fixed
> at 10 hours behind GMT. For 10 hours ahead of GMT, you'll need
> Etc/GMT-10.
> Unless you have a specific need for a timezone that has a fixed GMT
> offset (and doesn't adjust for daylight savings), you would be better
> off using the geographical zones (such as Australia/Brisbane).
> Kind regards,
> Phil
> --
> Phil Ross
> http://tzinfo.rubyforge.org/ -- DST-aware timezone library for Ruby
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> TZInfo-users mailing list
> TZInfo-users at rubyforge.org
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