The value of the On Field Update Invoke user property consists of three quoted parameters separated by a comma and a space, as follows:
"[FieldToCheck]", "[BusCompName]", "[MethodName]"
[MethodName] is invoked on the [BusCompName] business component when [FieldToCheck] is updated. If [FieldToCheck] is not defined, the method is invoked when the user saves the record.
You can optionally use a fourth parameter that defines a condition. If you define a condition, the method is only invoked if the condition evaluates to TRUE.