Thursday, July 14, 2005

International dates and times

It's sometimes challenging to work internationally, especially given we all use different paper sizes: letter, A4, etc...

We haven't yet found a solution for paper size, but since European countries and most of the commonwealth use the DIN (A4, A3, etc...) we're suggesting that the de facto standard is the one use by over 490m people vs. 290m in the USA...

On the times, here's a useful reference for people working with international colleagues: the International standard date and time notation

This page suggests to use the ISO 8601 (International Standards Organisaion) formats:

* for the dates YYYY-MM-DD
* and for tims hh:mm

The ISO 24h time format is commonly accepted. See this interesting note from the above referenced page:

A remark for readers from the U.S.:

The 24h time notation specified here has already been the de-facto standard all over the world in written language for decades. The only exception are a few English speaking countries, where still notations with hours between 1 and 12 and additions like “a.m.” and “p.m.” are in wide use. The common 24h international standard notation is widely used now even in England (e.g. at airports, cinemas, bus/train timetables, etc.). Most other languages do not even have abbreviations like “a.m.” and “p.m.” and the 12h notation is certainly hardly ever used on Continental Europe to write or display a time. Even in the U.S., the military and computer programmers have been using the 24h notation for a long time.

The old English 12h notation has many disadvantages like:

* It is longer than the normal 24h notation.
* It takes somewhat more time for humans to compare two times in 12h notation.
* It is not clear, how 00:00, 12:00 and 24:00 are represented. Even encyclopedias and style manuals contain contradicting descriptions and a common quick fix seems to be to avoid “12:00 a.m./p.m.” altogether and write “noon”, “midnight”, or “12:01 a.m./p.m.” instead, although the word “midnight” still does not distinguish between 00:00 and 24:00 (midnight at the start or end of a given day).
* It makes people often believe that the next day starts at the overflow from “12:59 a.m.” to “1:00 a.m.”, which is a common problem not only when people try to program the timer of VCRs shortly after midnight.
* It is not easily comparable with a string compare operation.
* It is not immediately clear for the unaware, whether the time between “12:00 a.m./p.m.” and “1:00 a.m./p.m.” starts at 00:00 or at 12:00, i.e. the English 12h notation is more difficult to understand.

Please consider the 12h time to be a relic from the dark ages when Roman numerals were used, the number zero had not yet been invented and analog clocks were the only known form of displaying a time. Please avoid using it today, especially in technical applications! Even in the U.S., the widely respected Chicago Manual of Style now recommends using the international standard time notation in publications.

Most of the world still use now an adapted version of the old German date format, as follows:


(In any case, the US format is both ambiguous and illogical...)

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