Section "InputClass"
    Identifier "Kensington Trackball"
    MatchProduct "Kensington Expert Mouse"

    Option "ButtonMapping" "1 2 3 5 4 6 7 8"

    Option "EmulateWheel" "True"
    Option "EmulateWheelButton" "8"
    Option "YAxisMapping" "5 4"
    Option "XAxisMapping" "6 7"
EndSection