A question to which calendrics have no ready answer is: which WEEK is it?

The closest thing to an "official" answer is put forth by the International Organization for Standardization in
ISO 8601

(Although the number of date formats accepted there recalls the gibe that standards are nice, there are so many to choose from.) The ISO definition, disregarding history, declares that the week begins with Monday. And the "first" week of the year is the first one which has more than half within the calendar year; and this definition appears to be followed in Sharp software. Putting this another way, the first week contains the first THURSDAY of the year, and this, being
Saturday, November 21, 2009
is
Week 47 of 2009

or in the format which Emacs tell us is "popular in Europe"
2009-W47-6

If we continue to accept that Sunday begins the week, the analogous principle tells us that it is
Week 46 of 2009

Others, however, will maintain that "week 1" is the week containing January 1st. Following the ISO Monday standard, this makes it
Week 47 of 2009

And using a Sunday standard
Week 47 of 2009

Another view is that "Week 1" begins with the first Sunday (or Monday) in January. Therefore, reckoning from Sunday, this is
Week 46 of 2009

or from a Monday reckoning
Week 46 of 2009

This also raises the question of whether "odd" days at the beginning of the year are "Week 0" or to be counted as the last week of the previous year, as in the ISO schemes above.

Finally, a method sometimes attributed to Hewlett-Packard software, and also used in the Astroclock program, just counts off every seven elapsed days of the current year. This makes it
Week 47 of 2009

This leaves us with the "week of month" in question. If we adopt an ISO semiweek style definition, and start with Monday, this gives us
Week 3 of November
and starting from Sunday
Week 3 of November

If we start with the week including the first of the month, and reckon from Sunday
Week 3 of November
or from Monday
Week 4 of November

Finally, starting with the first Sunday of the month makes it
Week 3 of November
and from the first Monday
Week 3 of November


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