TriggerCalc is the add-on you need if you want to make calculations involving ACT! fields. Whether you need to add 2 fields together or do more complex calculations, TriggerCalc is what you need. It is mainly designed to be used in conjunction with the ACT trigger feature which allows to launch a program when entering or exiting a field. This way, you can automatically re-start the calculation when one of the fields involved in it is modified.
This add-on is very simple to use, no user interface! All you need to do is enter your calculation at the end of the command line like in:
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 30 functions.