If the AllowRunTimeSummaryChange option is enabled, an end-user can change the data field's summary type by clicking its header (see the image below):

If the ShowSummaryTypeName option is enabled, the summary type is displayed within the field's header.
Changing the field's summary type raises the DevExpress.XtraPivotGrid.PivotGridField.SummaryTypeChanged event.
Note
This option is not supported in OLAP mode.