I got the linear/least squares autoregression fits (equations) approximating IOB for the Tandem t:slim, Animas 2020, Medtronic 522, and Medtronic 530G pumps. The order of the polynomials range from 4-7, and all of the fits converge in MATLAB. The Medtronic 530G had the closest fit and the nicest curve, in my opinion, but who knows if it is the closest physiological IOB approximation. I am testing out the equations right now. Will be done in 15 minutes and will be posting to OpenAPS dev group.