The RULE TYPE column

David Keegel djk at
Fri Jul 21 23:30:52 UTC 2006

On Fri, Jul 21, 2006 at 02:50:57PM +0200, Srdjan Krajnalic wrote:
> Hi,
> Unless I'm missing some of the data files, the only rule TYPE ever used is
> "-" 

You can find in tzdata, which defines what TYPEs are
supported.  Currently they are: even odd uspres nonpres/nonuspres.

The even/odd types were used in South Australia, which used to look
like this (snippet taken from tzdata96a.tar.gz):

# South Australia
Rule	AS	1971	1985	-	Oct	lastSun 2:00s	1:00	-
Rule	AS	1986	only	-	Oct	19	2:00s	1:00	-
Rule	AS	1987	max	-	Oct	lastSun 2:00s	1:00	-
Rule	AS	1972	only	-	Feb	27	2:00s	0	-
Rule	AS	1973	1985	-	Mar	Sun>=1	2:00s	0	-
Rule	AS	1986	1989	-	Mar	Sun>=15 2:00s	0	-
Rule	AS	1990	1994	even	Mar	Sun>=18 2:00s	0	-
Rule	AS	1990	1994	odd	Mar	Sun>=1	2:00s	0	-
Rule	AS	1995	max	-	Mar	lastSun 2:00s	0	-
The underlying reason for even/odd usage in this rule is that the
Adelaide Festival of the Arts is in March of even years since 1960.

Since there were only 5 years of this even/odd algorithm (and it is not
expected to reappear in future), it was decided to just hard code the
dates for those 5 years, so that yearistype would not be required for
this rule.

While the TZ database does not currently use year types, it is always
possible that some juridiction in the world will decide to have daylight
saving rules which are different every 2 years, or every 4 years, or
some other scheme that will require extending yearistype.

 David Keegel <djk at>
 Cybersource P/L: Linux/Unix Systems Administration Consulting/Contracting

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