http://forum.deltamotion.com/viewtopic.php?f=12&t=81

There isn't much we or Stuart can do. The system will not retract as fast as desired. These problems are caused by people use flow calculations to calculate speeds instead of the VCCM equation or better yet a real simulator.

Stuart actually does a pretty good job of tuning the system. It is tracking within about 0.001 inches while extending at a constant speed. See the plot at the bottom of the thread. The color code for the lines is in the bottom left.