In computing, a trackball is a pointing input device. It consists of a ball held by a socket containing sensors to detect a rotation of the ball about two axes. It is like an upside-down mouse with an ball that sticks out. The user rolls the ball with the thumb, fingers or the palm of the hand to move a cursor. They are currently only made by 3 major companies: Logitech, A4Tech and Kensington.[source?] Microsoft also used to be a major producer. Large trackballs are sometimes seen on computerized special-purpose workstations, such as the radar consoles in an air-traffic control room or sonar equipment on a ship or submarine.