The ScheduleSettings of the XamScheduleDataManager has a FirstDayOfWeek property. There is also a FirstDayOfWeek on the Resource. When resolving the FirstDayOfWeek, the controls look at the FirstDayOfWeek of the CurrentUser of the XamScheduleDataManager and then check the ScheduleSettings if the Resource didn't have a value and then ultimately fallback to the culture information provided by the DateInfoProvider of the XamScheduleDataManager.