tzdata 2003e: imperfections (DST rules)

Oscar van Vlijmen ovv at
Mon May 17 20:37:30 UTC 2004

> From: "Olson, Arthur David (NIH/NCI)"

> Remember that the Rules tell when DST transitions happen; in the above case,
> the Rule that's valid is one that specifies the last transition before May
> 2004, which is assumed to be in effect in perpetuity.

Excerpts from the zic.8 documentation file:

     A rule line has the form
          Rule  NAME  FROM  TO    TYPE  IN   ON       AT    SAVE  LETTER/S
     TO      Gives the final year in which the rule applies.  In
             addition to minimum and maximum (as above), the word
             only (or an abbreviation) may be used to repeat the
             value of the FROM field.
     The fields that make up a zone line are:
          Zone  NAME                GMTOFF  RULES/SAVE  FORMAT  [UNTIL]
     UNTIL The time at which the UTC offset or the rule(s) change
           for a location.  It is specified as a year, a month, a

The Rule and Zone (continuation) lines from the example are:

Rule    ROK    1987    1988    -    Oct    Sun<=14    0:00    0    S
            9:00    ROK    K%sT

If I am interpreting the documentation correctly, then the last Zone line
says that there is a Rule "ROK" in effect, but for dates after Sunday
October 09, 1988 no Rule can be found. The DST rules were changed, so,
strictly speaking, and according to the documentation, there should be a new
Zone line.

For users of the TZ software there is no problem I guess, but developers who
can only use the database files, encounter minor problems interpreting the

Oscar van Vlijmen

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