Download and run DIVew from Logitech. It will show you the axis and input from all of your USB game controllers, keyboard and mouse.
This product site for the Precision Joystick Controller BU0836 reccomends using it to check your output after building your joystick. Unzip and run it. There is no install, it just displays the output of all your devices. If you are seeing noise or bouncing on your axis from DIView it can be something in this list:
1. joystick axis potentiometer.
2. a bad USB port on your PC.
3. wrong USB port to have your device in.
4. wrong speed USB devices ganged together.
5. not enough power to your USB port or fluctuating power while playing the game.
6. processing conflicts during the game possibly due to one or several of the above problems including USB bus resets.
If you run DIView while your USB devices are sitting idle with no game controller software running and there is no bounce(noise) then you may be having processing conflicts and or power problems for that port. If you see bounching on an axis then the potentiometer is old or something in the list. My potentiometers don't bounce but occasionly during game play I notice bus resets. Thats when you seem to loose calibration or control of your axis. Who knows what causes bus resets during the game.....
http://www.leobodnar.com/products/BU0836/DIView.zip