Hi, Ok, I just decided I make the script generate a second graph. Updated script is attached, new sample graph is at http://www-user.rhrk.uni-kl.de/~nissler/rate_control_sample_graph2.ps I guess from the second graph we can see that the integration interval is too large. I think I should try increasing the proportional coefficient and decrease the integral coefficient. What do you think? Control theory people please speak up :-) Mattias