By default, the DisplayWeekNumberAs property is exISO8601WeekNumber, which indicates that the week number is displayed according to the ISO8601 standard, which specifies that the first week of the year is the one that includes the January the 4th. The ShowWeeks property specifies whether the week number header is shown or hidden. The FirstWeekDay property specifies the first day of the week where the week begins.

The following screen show shows the calendar while using the DisplayWeekNumberAs property on exISO8601WeekNumber ( default ):

The following screen show shows the calendar while using the DisplayWeekNumberAs property on exSimpleWeekNumber: