You are offerding on a Mouse Master for the Atari ST computer. This device will allow you to effortlessly switch between your Atari St mouse and joystick. This device does not allow for use of both mouse and joystick simultaneously. I really liked this device because it saved me the trouble of constantly plugging and unplugging the mouse/joystick for game play. This also prevents wear and tear on the joystick/mouse ports which are known to fail from excessive plugging and unplugging. This item was working flawlessly on my system at the time of take down however it is being sold as is without guarantees or warranty. No refunds/returns. Local pickup available.