The ShowWeeks property retrieves or sets a value that indicates whether the weeks header is visible or hidden. The DisplayWeekNumberAs property specifies the way the control displays the week number. Use the ShowNonMonthDays property to specify whether the dates that are not part of the month are visible or hidden. The Background(exWeeksHeader) specifies the visual appearance for the weeks header in a calendar control. The Background(exWeeksHeaderForeColor) specifies the foreground color to show the weeks in the header.

In [ISO8601], the week number is defined by: 

• weeks start on a monday
• week 1 of a given year is the one that includes the first Thursday of that year. (or, equivalently, week 1 is the week that includes 4 January.)