>Cetin I need it for an app for timesheet's the client's has Monday as FDOW

Yes I see but it only effects if you set related functions' nFirstDayOfWeek parameter to 0. So you don't need it IMHO. ie:

set fdow to 3 && Set tuesday
? dow(date()) && Today is Tuesday - returns 3, Sunday is default
? dow(date(),0) && returns 1, this uses set fdow
? dow(date(),set('fdow')) && returns 1, this uses set fdow
? dow(date(),3) && Same as before w/o using set fdow
? dow(date(),2) && W/o Setting FDOW to Monday, uses Monday as FDOW

Cetin