[tz] 1981/2 Singapore+Malaysia switch from GMT+0730 to GMT+0800

Robert Elz kre at munnari.OZ.AU
Tue Nov 22 23:39:17 UTC 2022

This press release was discovered, and brought up in another forum by
Geoff Clare.

It conflicts with the data in the Asia/Singapore and Asia/Kuala-Lumpur


That puts the change as being from
	23:29:59 Dec 31, 1981 -> 00:00:00 Jan 1, 1982
whereas tzdata (going back to quite ancient versions) has the transition
	23:59:59 Dec 31, 1981 -> 00:30:00 Jan 1, 1982

The version from the web page makes more sense to me (as in that
is how I would have done that transition) but that does not mean
that it is necessarily correct.

Nothing there shows a copy of the actual gazette notification by the
President (of Singapore in that case, but I think we can safely assume
that it was done the same as in Malaysia) which would be the actual
specification, but that 2015 press release says it happened as described
that it would happen in the 1981 press release which is included there.

The "asia" file just says of this transition:

                        7:30    -       +0730   1982 Jan  1
                        8:00    -       +08

which is correct in a sense for either version of when the transition
occurred, and perhaps raises a general question of when a step forward
takes place at the boundary between two days, does it more often delete
the last part of the previous day or the first part of the next?

I can find nothing in my tz list archives that says anything at all
about this transition - the earliest message with any specific
content about Singapore I could see was a Jan 2004 message from
Mok Ly Yng (forwarded to the list by ado@), but that's really about
earlier transitions - this one was already in the data (just with SGT
instead of +0730 and +08).

There's also a long Sept 2014 discussion about a zdump bug that this
particular transition, as defined by zic, revealed, and a shorter
discussion about the SGT removal in Sept 2018 - but that's all I
managed to find about Singapore.

While not about the Singapore/Malaysia zones themselves, even older
data that appears on the list (ie: looking at diffs patches, and updated
zone files) shows that in 1996 this transition was believed to have
happened in May 1982 (which seems to be from Shanks).   That altered
in Dec 2003, in a change described as:

 * Fix several Malaysia and Singapore entries before 1983.
   Among other things, they enjoyed 20-minute DST from 1933 to 1936,
   and we have more-accurate dates for WWII transitions.
   (Thanks to Mok Ly Yng for this info.)

which notably does not mention the change moving from May 1982 -> 1 Jan 1982
but that change was made in that version.   Nothing appears to have
happened since.

I suspect it would be correct to change the first of those lines
to be

                        7:30    -       +0730   23:30 1981 Dec 30

but I am no authority on that.


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