Re: Why not 13 months? (Was La Systeme Metrique)

Markus Kuhn (
17 Sep 1995 13:34:53 +0200

Doug Weller ( wrote:

> Who doesn't believe them? It's just that they may only be relevant
> to religious people. If seems to that for some people the week
> begins on Sunday, for others on Monday, and both can be correct in
> their contexts (it also seems that the ISO standard says Monday is
> the first day, so perhaps there is a slow movement
> from Sunday to Monday).

In case anyone is interested in the ISO standard for date, time, week
numbers, etc., please have a look at


or download with anonymous ftp from the file

Monday has been chosen as the first day of the week because this
simplifies commercial and industrial planning. Especially Christian
religious communities have protested against the change from the old
few that the Sunday is the first day of the week. The ISO standard now
especially notes that the calendars of religious communities are not
affected by this standard which is used for commercial calendars and
industrial planning in most parts of the world.

Also the definition that week number one of a year is the first week
which has the majority of its days in the new year (i.e. which
contains the first Thursday of a new year) has been chosen in order to
simplify industrial planning which is especially in Europe organized
per week.


As we are talking about date standards:

For those of you wondering, what the professional and correct way of
writing a calendar date in network publications is:

The international standard date notation is: YYYY-MM-DD

For example, February 4, 1995 is written as 1995-02-04. This notation
is standardized in International Standard ISO 8601.

Other commonly used notations are e.g. 2/4/95, 4/2/95, 4.2.1995,
04-FEB-1995, 4-February-1995, and many more. Especially the first two
examples are dangerous, because as both are used quite often and can
not be distinguished, it is unclear whether 2/4/95 means 1995-04-02 or

Advantages of the ISO standard date notation are:

- easily parsable by software (no 'JAN', 'FEB', ... table necessary)
- easily sortable with a trivial string compare
- language independent
- can not be confused with other popular date notations
- consistent with 24-h time notation hh:mm:ss which comes also
with the most significant component first and is consequently
also easily sortable (e.g. write 1999-12-31 23:59:59).
- short and has constant length (makes keyboard data entry easier)
- identical to the Chinese date notation, so the largest cultural
group (>25%) on this planet is already familiar with it.
- 4-digit year representation avoids overflow problems after

In shell scripts, use

date "+%Y-%m-%d %H:%M:%S"

in order to print the date and time in ISO format. In C, use the
string "%Y-%m-%d %H:%M:%S" as the format specifier for strftime().

The year 2000 might be a good opportunity to change to a common
worldwide date notation on 2000-01-01, because date notations like
02/03/00 will look strange anyway.


Markus Kuhn, Computer Science student -- University of Erlangen,
Internet Mail: <> - Germany
WWW Home: <>