There are many variations on the layout and labelling of keys. Extra numeric keys may be added, as may special-purpose function keys, whose effects can be defined by programs in the computer. The graphics tablet is an input device in which a stylus or cursor is moved, by hand, over a flat surface. The computer can keep track of the position of the stylus, enabling the operator to input drawings or diagrams into the computer. The joystick signals to a computer the direction and extent of displacement of a hand-held lever.
Light pens resemble ordinary pens and are used to indicate locations on a computer screen.
Scanners produce a digital image of a document for input and storage in a computer, using technology similar to that of a photocopier.