[tz] EU Public Consultation on summertime arrangements

Paul Eggert eggert at cs.ucla.edu
Mon Jul 9 22:59:40 UTC 2018

Clive D.W. Feather wrote:

> The term in the Directive is "summer time", not "daylight saving time".

OK, it's changed to "summertime" in the revised draft (attached). I omitted the 
space between "summer" and "time" because that's how it's spelled in the 
questionnaire. The attached draft also reflects your other comments. Thanks.
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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 summertime arrangements. 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 twice-yearly clock 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 EEA countries, membership candidates, potential candidates, Schengen area, and other countries not in the EU that decide to make a related change. This document would be purely informative, with no authority behind it.

3. If the EU abolishes the twice-yearly clock changes, the resulting time zones should be considered standard time, not permanent summertime, to avoid conflicts with existing computer standards in widespread use. The notion of permanent summertime 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, many people would naturally 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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