Precision Flight Serial CAT I and Microsoft Flight Simulator 9 (2004) - Manual (Page 14)

Set Up Guide for Serial CAT1 and FS2004 Page 14
a. If you rudder trim is not responding, it means that it is not a separate channel and is
connected to the rudder pedals instead. Disable the rudder trim check and set the rudder
trim to the center with your rudder pedals.
If your rudder trim is responding:
a. Click on Select button under the Rudder Trim Axis. This should say Set Automatic
now.
b. Turn your Rudder Trim knob the way to the Left. Click on the Set left most limit.
c. Turn your Rudder Trim knob all the way to the Right. Click on the Set right most limit.