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INT 33h,  13h (19)       Set Double Speed Threshold

    Defines the threshold speed.

       On entry:      AX         13h
                      DX         Threshold Speed in Mickeys/second

       Returns:       Nothing

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    Function 13h sets thethreshold speed for doubling the cursor's motion on
    the screen. Using function 13h makes it easier to point at widely
    separated images on the screen.

    DX defines the mouse's threshold speed. If the mouse is reset by a call
    to function 0, a default value of 64 Mickeys per second is assigned. If
    the mouse moves faster than the value of DX, cursor motion doubles in
    speed. The threshold speed is set until function 13h is called again or
    until the mouse is reset by function 0.

    Once Your program has turned on the speed doubling feature, this feature
    is always on. However, the program can effectively turn this feature off
    by setting the threshold to a faster speed than the mouse can physically
    move (for example, 10,000).