Makes it possible for you to select a mathematical operation to create a computed field. This dialog box is displayed when you choose Calculations in the Report Expression dialog box.
Note: 

Depending on the setting of the _REPORTBUILDER system variable, this dialog may be replaced by an alternative user interface. For more information, see _REPORTBUILDER System Variable. 
 Reset

Specifies the point at which to reset any cumulative calculations. The default value is "End of Report".
Note: If you have specified data groups in the report, Detail bands, or target alias expressions for Detail bands, the Reset based on list displays those items.
Calculate
Specifies additional calculation operations that can be applied to the values of a Field control expression to obtain the value rendered in the output.
 Nothing
 (Default) No additional calculations are performed. The result of the Field expression is directly passed to the report engine for output.
 Count
 The value displayed is a count of the number of times the expression has been evaluated for the records traversed thus far. (The Field expression is not evaluated.)
 Sum
 The value displayed is a running total of the values of the Field expression for the records traversed thus far.
 Average
 Computes the arithmetic mean of the value of the Field expression for each record traversed thus far and displays the results.
 Lowest
 Displays the lowest value of the expression for a group, page, column, report, or Detail band, depending on the option selected in the Reset list and uses the value of the first record in the group in the expression. When a lower value is encountered, the expression's value changes accordingly.
 Highest
 The value displayed is the highest value of the Field expression evaluated for the records traversed thus far.
 Standard deviation
 Computes the square root of the variance of the evaluated Field expression for each record traversed thus far and displays the results.
 Variance
 Measures the degree to which the evaluated Field expression value varies from the average for the records traversed thus far and displays the result.