Clicking the Calculated Item... item in the Fields, Items, & Sets drop-down menu. Add the Calculations ribbon group to enable this menu (refer to the Lesson 1 - Create a Simple Spreadsheet topic for details on how to provide your application with a Ribbon UI).
In the Name and Formula boxes of the Insert Calculated Item dialog, end-users can enter the name (PivotItem.Caption) and formula (PivotItem.Formula) for the calculated item.
The calculated item's formula can contain constants and references to other items in the same field to which the calculated item belongs. End-users can select the desired item in the Items list and click the Insert Item button to include the item reference to the formula.
Clicking the Add button adds the calculated item to the target PivotTable field.
End-users can modify the existing calculated item by selecting the desired item in the Name drop-down list and changing its formula. The calculated item's name cannot be modified from this dialog.
Clicking the Delete button removes the selected calculated item.