To assign the result of an arithmetic function

From the Service Interfaces Editor Assignments pane, right-click, then click New Assignment from the popup menu.
From the Assign to drop-down list, click the field to which you want to assign a value.
Do one of the following:
- From the Field 1/Operand 1 drop-down list, select a field.
- Type a numerical value into the Field 1/Operand 1 field.
From the Function/Operator drop-down list, select one of the following operators:
- +
- -
- /
- *
Repeat step 3 for the Field 2/Operand 2 field.
Click OK.

Note:

Fields that are part of an array appear on the Field/Operand drop-down lists with a subscript. The default subscript is the total number of occurrences of the field. To specify a specific occurrence, edit the subscript in the Field/Operand field. If you want to specify all occurrences, type an asterisk (*) as the subscript.
Any condition defined for the assignment appears in the Assignment Condition box at the bottom of the Assignment dialog box.