I'm working on extracting parts of a filter model and things aren't working as expected. I've attached the workbook. First on line 2 I've created a filter model which takes the form of a Transfer Model. Then on line three I extracted the denominator and called it u. So then I want to get all the poles isolated. Actually, I know there is a function for this but this is just a precursor to understanding how to manipulate and extract things from the transfer function for further work. Nevertheless, in line 4 I tried to extract all the poles from u. So I don't get all the poles, but instead I get the coefficient in the numerator of the transfer function. I don't even know how that got into u as in line 5 I'm showing everything in u and that coefficient isn't even there! So, I think there is some sort of bug in the list manipulation functions associated with these transfer functions. Anyone have any insight into this?