This is an old thread, but it came in VERY handy today. And yes, to confirm the quote above: the LOOKUP_INST() function is designed to accept parameter values that are of type "real number" only. Unfortunately, even though family table instances can be defined by parameters that are integers, real numbers, or YES_NO booleans, the LOOKUP_INST() function will only accept real numbers. I have confirmed this with PTC tech support. They classify it as a "limitation."dhbigelow said:I belive this function ONLY works with Real Numbers.