date function returns February 20 1900 when use type today’s date 11/09/2012
even if you enter it in this format weeknum(2012-09-11;1)
The date/time function need dates enter as date.
i.e. weeknum(2012-09-11;1) you are getting the week of 1905y06m14d (algebraic sum of 2012 - 09 - 11 = 1992 days after 1899y12m31d)
you must use WEEKNUM(DATE(2012;09;11);1)
also WEEKNUM(“2012-09-11”;1), but this form (date as text) can come in troubles, only can be used when no other interpretation of text is possible (locale language), and with direct references WEEKNUM(B15;1), Not with range functions WEEKNUM(SUM(B10:B15);1), better avoid.
Calc Guide 3.4 (spreadsheets): ODT, PDF. Page 376 date & time functions. https://wiki.documentfoundation.org/images/b/b7/CG34-CalcGuideLO.pdf
Could the above explanation INCLUDING the samples be added to the help file? I would regard as and added value.
I had the format for the cell as date when it was changed to number it corrected the problem still would like to see better help explanations for functions any one recommended a book or web site