While you cannot insert custom functions directly in decisions, you can easily create a ruleset to wrap the custom function and pass in and out of the ruleset.  For example, here is a simple custom function: I have wrapped that custom function in a simple ruleset that has nothing but an assignment:   Then I place that ruleset in a decision.  This enables me to pass local variables d1 and d2 to the custom function and receive the sum.    I hope this helps:       ... View more