Abstract: A pointing device is provided for use with a computer and display screen. The line of sight of the pointing device is determined with reference to one or more electromagnetic radiation sources located adjacent to the screen. The pointing device includes a processor for receiving signals from a sensor within the device, processing the signals with respect to calibration data to generate co-ordinate data which identifies a location on the screen at which the pointing device is directed, and outputting the co-ordinate data for transmission to the computer. Thus, dedicated software does not need to be installed on the computer to enable it to interact with the pointing device. Methods of operating the pointing device are also described, together with methods of calibration. According to a further aspect, the device sensor is mounted in the pointing device with the centre line of its field of view at an acute angle with respect to the reference axis of the device.