TriggerCalc is the add-on you need if you want to make calculations involving ACT! fields. It is mainly designed to be used in conjunction with the ACT trigger feature which allows to launch a program when you exit or change a field. This way, your calculated fields are always up-to-date.
TriggerCalc allows to run multiple calculations at once for the current contact, current lookup or all contacts. It also works with companies and groups.
There are 2 versions of TriggerCalc. The standard version allows to make calculations using operators (like +, -, *, \, AND, OR, etc.) while the Pro version gives you the ability to use more than 50 functions.
TriggerCalc uses a convenient wizard to set up your triggers and calculations. (see screenshot).