Aspose::Cells::Pivot::PivotField::SetBaseItemPosition method. Represents the item in the base field for a Custom calculation. Valid only for Data fields. Because PivotItemPosition.Custom is only for read,if you need to set PivotItemPosition.Custom, please set PivotField.BaseItemIndex attribute in C++....field for a custom calculation. Valid only for data fields. Because...Because PivotItemPosition.Custom is only for read,if you need to...