DP_DateExtension:
Alternate First Day of Week Examples

The round(), ceil() and floor() methods consider the starting day of the week as set in Date.FirstDayOfWeek (default is "0" which is Sunday):

The diff() method provides three distinct methods for determining differences in dates. Two of them, "Logical" and "Complete" alter their bahavior based on the value of Date.FirstDayOfWeek. The methods are:

• Logical: This method results in a difference for any change past the specified FirstDayOfWeek. For example if FirstDayOfWeek is set to "1" (Monday) then there is a one-week logical differnce between Sunday and Tuesday.
• Complete: This method returns differences only for whole, complete weeks starting on the specified FirstDayOfWeek and ignores partial weeks before or after.

The best way to understand these options is through examples: