jrl jrl at
Tue Feb 22 13:19:26 UTC 2011

I don't think I made myself clear... 

According to the documentation, the Rule says that the time change ran ends on the Sunday before the 15th for the years 1978, 1979, and 1980.   The documentation should indicate what you say is true:

Rule    Macau   1978    1980    -       Oct     Sun>=15 0:00    0       -

I read the line above as follows:

In October 1980, the rule changed to standard time.  So at this point, refer to the Zone.

The Zone says:
                        8:00    Macau   MO%sT   1999 Dec 20 # return to China

Meaning use the Macau rules until Dec 20, 1999

There are no Macau Rules after October of 1980.

SO... in my mind it means we revert to the overall rule of the Zone for that period.  The Zone says it is in effect from 1912 through 1999 - use Macau rules.   If there are no rules, then revert back to the rule of the Zone.  

That makes you correct in that the Zone is 8:00 offset from GMT not 7:34:20 LMT.

What doesn't make sense if why a set of Rules is used that ends prior to the end of the period used by the zone.  It's a moot point but it confuses the flow.

Perhaps a "max" in place of the 1980 would make this more clear.  It would not interrupt the flow because the Zone says ignore Macau after 1999.  The max is used elsewhere.  Why is it NOT used here?

From: kre at munnari.OZ.AU [kre at munnari.OZ.AU]
Sent: Tuesday, February 22, 2011 8:00 AM
To: tz at
Subject: Re: Macau

    Date:        Tue, 22 Feb 2011 11:14:18 +0000
    From:        jrl <jrl at>
    Message-ID:  <E468A544C5BEF74DBF22CAAB3FD50DE810F47BBB at UNIVERZ.terraatlas.local>
  | What is the correct rule for Macau from 1980 through 1999?
  | Did they return to LMT?

I wonder if there is any way we can make the documentation clearer
that the rules do not specify intervals, but transition points.

People keep asking questions (like this one) that make no sense at all
if the rules are interpreted correctly, but would be perfectly legitimate
if the rules were doing something like "specifying the period when summer
time applies".

Since this mistake is so commonly made, it must be a problem with the tz
documentation.   Unfortunately, I can't see it (which is often true when
someone who knows the answer tries to see why others cannot see it).

Does anyone have any ideas how we can make this clearer?   Is the problem
that people are just reading the data files, and ignoring the documentation?
Do we need to add some explanatory comments in every data file?


ps: the Macau rules say that the last time there was a std/summer time
transition in Macau was the 3rd SUn in October, 1980, since then the
only change has been the change of time zone abbreviation when Macau
became part of China again.   So, no, it dod not revert to LMT, there simply
were no more transitions - and once you understand that the rules are
used to specify transition points, this is really all very obvious.

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