Ian Abbott abbotti at
Tue Feb 22 18:38:12 UTC 2011

On 22/02/11 17:25, jrl wrote:
> Robert,
> All this said Robert, your clarification is helpful, and I thank you 
> for that.
> Architecturally, my picture of a Zone (transition), as an individual 
> element/object/entity for any given period of time will have a fixed 
> beginning and ending.  The end is when the new transition starts or 
> for lack of one, it ends here and now.
> From that point of view, "max" is appropriate because for that entity 
> (one with a fixed beginning and ending), the process of determining 
> the transition via a given date, will discard the old object for the 
> new one, making the previous "max" valid but for a transition that is 
> no longer valid.
> Consider the picture as it would look in 1999, before the PRC
> transition, [for Macau].
> --- as of Nov 1999 ---
> Rule	Macau	1978	1980	-	Apr	Sun>=15	0:00	1:00	S
> Rule	Macau	1978	max	-	Oct	Sun>=15	0:00	0	-
> Zone	Asia/Macau	7:34:20 -	LMT	1912
> The word "max" would be entirely appropriate.   By your current 
> listing, when PRC became relevant, it was then necessary to remove
> the "max" and put in something else... say 1980.  I would argue to 
> leave it as it would have been at that time. The addition of the new
> transition would negate the effect of the "max" and there would be no 
> need for a change at that time.

For the "TO" field, "max" could be replaced with "1980" as soon as it
became known that daylight savings time no longer applied after 1980.

Setting "TO" to "max" indicates there is an "empty" transition (from
standard time to standard time) every year in October from 1981 onwards
until the Macau rules are no longer used (after 1999).  Setting "TO" to
1980 gets rid of these useless empty transitions.

The Asia/Macau zone indicates that the "Macau" rules applied from 1913
until 1999 Dec 20 with a GMT offset of 8:00 and a format of "MO%sT".
This is the offset and format that is used before the first transition
and after the final transition.

One thing that is not clear to me at the moment is how the "%s" part of
a zone's format is expanded before the first transition and after the
final transition of a rule set.  But I'm sure this would become clear if
I studied the zic source code a bit more!

> Regards,
> Jamie
> -----Original Message-----
> From: kre at munnari.OZ.AU [mailto:kre at munnari.OZ.AU] 
> Sent: Tuesday, February 22, 2011 10:44 AM
> To: tz at
> Subject: Re: Macau
>     Date:        Tue, 22 Feb 2011 13:19:26 +0000
>     From:        jrl <jrl at>
>     Message-ID:  <E468A544C5BEF74DBF22CAAB3FD50DE810F48C13 at UNIVERZ.terraatlas.local>
>   | Meaning use the Macau rules until Dec 20, 1999
>   | There are no Macau Rules after October of 1980.
> Yes.
>   | SO... in my mind it means we revert to the overall rule of the Zone
> No, no rules means no transitions, the time just continues forward
> (like the clock on your wall) without any strange jumps.   Whenever the
> time jumps, we need a transition point, the rules say when those transition points appear.
>   | If there are no rules, then revert back to the rule of the Zone.
> Where do you think the documentation says that?   Because if there is
> somewhere, we need to fix it, because that's not how it works at all.
> The rules give the method for finding the transition points, when there is no transition point, time just moves forward, as time always has.
>   | 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.
> Because there was a period when there were transitions, and that period ended, the rules cover the period of transitions.
>   | Perhaps a "max" in place of the 1980 would make this more clear.
> No, just the opposite.  We use "max" when we have transitions that are continuing into the future, to some (as yet) undetermined future time.
> When we know when the transitions stopped occurring, we say so, that is what makes things clear.
> Once again, the point of the rules is to provide a method by which we calculate the points at which local wallclock time experiences a 
> non-continuity, and that's it.   Nothing else is reasonably possible,
> as these things are not necessarily nice nested "go forward and back"
> operations that could be expressed using other means.
> kre
> ps: you said "the time change ran ends on the Sunday before the 15th for the years 1978, 1979, and 1980" whereas the rule you quoted in the earlier mail was "the first sunday on or after the 15th" (Sun>=15) (a way of saying "the third sunday") - I assume the "before" in your message was just a typo/thinko.

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

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