This is really, "if we can't have math functions between fields how about a work around".
Situation. Many sales operations pay commission to their people based on the total value of sales. They would like to be able to report this information from ACT!
Problem. There is no method of doing this in ACT!
Work Around; We DO have the ability to set percentages associated with sales stages, so you could add a sales stage called "Commission" as a final stage and set the probability to 10% (if that's the commission rate you pay). The commission payable is now in the Weighted total field. Not ideal, but usable, up to the point when you mark the Opp as Closed/Won.
Next Problem: When you check an opportunity to Closed / Won, the probability is automatically set to 100%.
Solution: Make the Closed/ Won probability editable.
You would then be able to mark Opps as Closed/Won and the Weighted Total would be the Commission Payable.