Changing Summary Type
Pivot Tables can perform different calculations against data (for instance, calculating sums, averages, maximum and minimum values, etc.).
To specify which calculations Pivot Table should perform against its data, invoke the Data Field Summary Change Menu by left-clicking a data header and choose the appropriate function type.
To allow end-users to change the summary type at runtime, set the PivotGridFieldOptions.AllowRunTimeSummaryChange to true.