The SAM (Switch Adapted Mouse) is a high quality trackball that accepts any switch that ends in a 1/8″ plug. The user can operate the trackball and use an external switch for the mouse click. SAM is plugged in where your regular mouse goes. The switch inputs are clearly marked as to which buttons they are. The middle button/switch input is called a drag lock. It locks the left button down until you subsequently hit any button. this allows the user to drag without being required to hold any button/switch down during the drag. A Utilities disk comes with the SAM and after installation on your computer gives you the ability to add more functionality to the buttons.