A pointing device is a human interface device that allows a user to input spatial (i.e., continuous and multi-dimensional) data to a computer. CAD systems and graphical user interfaces (GUI) allow the user to control and provide data to the computer using physical gestures by moving a hand-held mouse or similar device across the surface of the physical desktop and activating switches on the mouse. Movements of the pointing device are echoed on the screen by movements of the pointer (or cursor) and other visual changes. Common gestures are point and click and drag and drop. While the most common pointing device by far is the mouse, many more devices have been developed. However, the term mouse is commonly used as a metaphor for devices that move a computer cursor. Fitts's law can be used to predict the speed with which users can use a pointing device. Classification To classify several pointing devices, a certain number of features can be considered. For example, the device's movement, controlling, positioning or resistance. The following points should provide an overview of the different classifications. direct vs. indirect input In case of a direct-input pointing device, the on-screen pointer is at the same physical position as the pointing device (e.g., finger on a touch screen, stylus on a tablet computer). An indirect-input pointing device is not at the same physical position as the pointer but translates its movement onto the screen (e.g., computer mouse, joystick, stylus on a graphics tablet). absolute vs. relative movement An absolute-movement input device (e.g., stylus, finger on touch screen) provides a consistent mapping between a point in the input space (location/state of the input device) and a point in the output space (position of pointer on screen). A relative-movement input device (e.g., mouse, joystick) maps displacement in the input space to displacement in the output state. It therefore controls the relative position of the cursor compared to its initial position. isotonic vs. elastic vs. isometric An isotonic pointing device is movable and measures its displacement (mouse, pen, human arm) whereas an isometric device is fixed and measures the force which acts on it (trackpoint, force-sensing touch screen). An elastic device increases its force resistance with displacement (joystick). position control vs. rate control A position-control input device (e.g., mouse, finger on touch screen) directly changes the absolute or relative position of the on-screen pointer. A rate-control input device (e.g., trackpoint,