I'm now needing to use "List of" to get a list of a ID's from a found set. This is the first time I've required a summary field. Are they like unstored calculations in that don't have any overhead if they aren't referred to or accessed? Or is FileMaker going to be calculating the "List of" summary field behind the scenes whenever a found set is created? I only need it for a single script (it is otherwise never displayed or referred to), and I'll take another approach if it will have any performance impact outside of that script.