a target position aimed at by a gun in a computer - controlled gun shooting game is detected . data representative of the position of the gun aiming at the target are derived from x - and y - volumes . the data is subjected to analog - to - digital conversion to provide decimal values . the decimal values are translated to coordinate values which represent a position on a monitor screen on which the target is displayed . to perform the translation , the x - and y - volume data are derived while sequentially moving the gun to aim at two reference marks displayed at corner and center positions of the monitor screen . by multiplying a ratio of a distance between two reference marks on the screen to the gun moving distance to the decimal values , the target position is represented by coordinate values of the screen . with such a procedure performed prior to starting the gun shooting game , the target detection accuracy is preserved despite the position of the gun placed or the distance between the gun and the monitor screen .