The ReferenceGroupOffset is used to calculate what range of dates should be displayed by the group. It is used along with the ReferenceDate and CurrentMode when calculating the FirstDateOfGroup and LastDateOfGroup.
By default, the template of the Infragistics.Controls.Editors.CalendarBase contains a CalendarItemGroupPanel which creates CalendarItemGroup instances based on the Dimensions. It initializes this property such that the first displayed group has a ReferenceGroupOffset of 0 and therefore contains the ReferenceDate. All subsequent groups are offset positively by 1 so that they show the next group worth of dates. If you retemplate the CalendarBase to directly contain CalendarItemGroups then you must set this property. For example, you might have 3 groups whose ReferenceGroupOffsets are -1, 0 and 1. When the ReferenceDate is August 1 2008 and the CurrentMode is days, the group with -1 would display the dates for July 2008 and the group with 1 would display the dates for September 2008.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2