WEEKNUM(A1; 1) returns 11 when A1 is "9th of March 2008". Number of the week in the year, with a week beginning on Sunday (1, this is the default if Method is omitted.)
WEEKNUM( A1; 1) jout 11 as A1 "09 maart 2008" befettet. wikenûmer yn it jier, mei de wike begjinnend op snein (11)