The Sum of Field Values behavior adds the values from a group of fields. To add a sum rule, you will need to select the Rules menu.
Select the field you wish to add a sum calculation. You will then select the Add a rule drop down menu from under Value Rule and choose Sum of Field Values.
The Sum of Field Values rule works by setting the field value to the result of summing together the values from a set of fields whenever any of those values change.
Drag and drop fields from the Rule Tools to create the set of values to be summed.
A Sum of Field Values rule will be created to add up the ExtendedAmount column.
Add the following fields to the rule:
The MaterialsSubtotal will be updated every time that one of the ExtendedAmount fields change in naturalForms.