You will sometimes find that the "+" cursor in the lower right of the box will be unstable, (jitter).
Also the low end of the bars may show some jittery behavior. This is due to noise pickup of the potmeter wires. When the potmeter is turned for maximum (100kW ) resistance, the noise can easily be picked up from the wires to the game port. This will give unstable axis movement, and often gives different range after each calibration, as the PC sees variable range at the high resistance setting. As you can see from the wiring diagram, high potmeter resistance corresponds to right aileron, up elevator, right rudder, and idle throttle.
To minimize jitter, use shielded cable for each axis, from potmeter to gameport. Try to keep cables as short as possible, and keep them away from noise sources like switching power supplies.
Sometimes, poor contact of the potmeter wiper to the carbon resistance trace can cause jitter. There are special contact sprays for electronics that can help.
Connecting the unused outer contact of the potmeter to the middle contact can also help, as it avoids the "open contact" condition.
This diagram illustrates how to make your controls less sensitive for noise. Keep the unshielded ends as short as possible.