>The Calendar Year 2000 started on a Saturday and finished on a Sunday, thereby requiring 54 weeks or part-weeks on a Sun..Sat basis; this happens (in 1901..2099) at 28-year intervals, for any year containing a Tuesday February 29th. All other calendar years require exactly 53 weeks or part-weeks (52 is clearly insufficient for 52×7+1=365 days). The situation occurs equally often for weeks starting on any other day; but is different with the ISO 8601 definition of Week Number.
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>Calendar Year 2012 contains 54 weeks or part-weeks on a Mon..Sun basis, like all years with a Wednesday February 29th. Its days belong to three different ISO week-numbering years.
>
>
>From widipedia:
>
>Mutually equivalent definitions for week 01 are:
>
>the week with the year's first Thursday in it
>the week with 4 January in it
>the first week with the majority (four or more) of its days in the starting year
>the week starting with the Monday in the period 29 December - 4 January
>If 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in week 01. If 1 January is on a Friday, Saturday or Sunday, it is in week 52 or 53 of the previous year.
>The week number can be described by counting the Thursdays: week 12 contains the 12th Thursday of the year.
>
>The ISO year starts at the first day (Monday) of week 01 and ends at the Sunday before the new ISO year (hence without overlap or gap). It consists of 52 or 53 full weeks. The ISO year number deviates from the number of the normal year (Gregorian year) on, if applicable, a Friday, Saturday, and Sunday, or a Saturday and Sunday, or just a Sunday, at the start of the ordinary year (which are at the end of the previous ISO year) and a Monday, Tuesday and Wednesday, or a Monday and Tuesday, or just a Monday, at the end of the ordinary year (which are in week 01 of the next ISO year). For Thursdays the ISO year number is always equal to the ordinary year number.
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>Examples:
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>2008-12-29 is written "2009-W01-1"
>2010-01-03 is written "2009-W53-7"
>
>http://en.wikipedia.org/wiki/Week#Week_number

Tracy,

Why do you reply to me with this? It is just an additional useful information, or you do not agree with what I said, or ... ?