[tz] EU Public Consultation on summertime arrangements

Paul Eggert eggert at cs.ucla.edu
Mon Jul 9 18:46:05 UTC 2018

John Wilcock wrote:
> I'm surprised a consultation by the EU hasn't provoked more comment here.

It *is* summer....

> I'm not entirely convinced your second point is clear enough for bureaucrats not 
> familiar with all the underlying concepts to understand.

Yes, it can use some work. I rewrote that second point and am attaching a 
revised proposed comment, where it appears as the paragraphs numbered (3) and 
(4). This update also reflects Brian Inglis's remarks (thanks!), as part of the 
paragraph numbered (2) in the attached.

> Surely tz could/would simply define new Western, Central and Eastern European 
> Standard Time zones and assign the relevant locations to them

Yes, although this would be done indirectly, by updating the existing entries 
Europe/Berlin, Europ/Paris etc., rather than by defining new Zones. There won't 
be a problem fixing the UTC offsets for these entries. The only issues are (1) 
what time zone abbreviations the new timestamps will have, and (2) whether the 
new timestamps will be considered to be daylight saving time.
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I am commenting as coordinator of the Time Zone Database (TZDB) hosted by the Internet Assigned Numbers Authority[1]. This database is used by most of the world's cell phones and many of its computers to track time zones and daylight saving time. The comments below have been circulated on the TZDB mailing list and attempt to reflect consensus there.

Although the simplest thing for computing applications would to keep the EU rules unchanged, it would not be much of a problem to accommodate the abolition of daylight saving time changes in the EU, as has already been done in Russia and other countries. However, if such a change is done, the following technical points should be considered.

1. If timekeeping rules are changed, there should be at least a year's notice before the changes take effect. Otherwise there is a good chance that some computer-based clocks will operate incorrectly after the change, due to delays in propagating updates to software and data. The shorter the notice, the more likely clock problems will arise. For more about this, please see "Changes to the tz database"[2] and "On the Timing of Time Zone Changes"[3].

2. If the EU rules are changed, the EU should record in a public document its member states' related changes to civil time, so that interested parties can easily track European timekeeping changes. For best results, the document should also keep track of changes to civil time in membership candidates, potential candidates, Schengen area, and other countries not in the EU that decide to make a related change.

3. If the EU abolishes the twice-yearly clock changes, the resulting time zones should be considered standard time, not permanent daylight saving time, to avoid conflicts with existing computer standards in widespread use. The notion of permanent daylight saving time is not supported by the POSIX.1-2017 standard[4], which covers most of the computing servers in the European Union.

4. If the EU abolishes the twice-yearly clock changes, time zone names should be specified to help avoid confusion. For example, if France decides to stay on UTC +02 all year, the TZDB natural default will be to call France's new time zone "Eastern European Time (EET)", due to the long association between "EET" and UTC +02. The EU should suggest this terminology (or some other terminology, if it prefers) to help interested parties discuss and understand the new timekeeping clearly.


1. Time Zone Database, Internet Assigned Numbers Authority. <https://www.iana.org/time-zones>

2. Changes to the tz database. <https://data.iana.org/time-zones/tz-link.html#changes>

3. Johnson M. On the Timing of Time Zone Changes. 2016-04-23. <https://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/>

4. The Open Group Base Specifications Issue 7, 2018 edition, IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008). See section 8.3 "Other Environment Variables", under the variable "TZ" <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03>.

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