Detect the presence of finger or stylus on the screen.
works by interrupting matrix of light beams, capacitance changes or ultrasonic reflections
direct pointing device
Advantages:
fast, and requires no specialised pointer
good for menu selection
suitable for use in hostile environment: clean and safe from damage.
Disadvantages:
finger can mark screen
imprecise (finger is a fairly blunt instrument!)
difficult to select small regions or perform accurate drawing
lifting arm can be tiring