By default, Excel populates the data area of your PivotTable by applying the Sum function to any numeric field you put in the data area or the Count function to any nonnumeric field. But you can choose from many alternative forms of calculation, and you can add your own calculated fields to the table.
To switch to a different summary function, select any cell in the data area of your PivotTable. Then click the Field Settings button on the PivotTable toolbar (or choose PivotTable, Field Settings). Excel displays the PivotTable Field dialog box (refer to Figure 30-12). Select the function you want to use, and then click OK.