These three parts combined to provide a reasonable – if not perfect – degree of accuracy, and allowed the user to effectively use the light gun from the comfort of an armchair.
The main component of the Stack Light Rifle System is the electronic target pistol that is connected to the computer by a generous length of lead.
On the ZX Spectrum version the connector contains two chips and a couple of simple components to interface the main electronics inside the gun to the computer.
Light coming down the barrel is focused by a small plastic lens onto the photo-diode, and the device is sensitive enough to detect the changes in intensity of the picture.
As the computer receives the pulse from the Light Rifle it compares the value of its scan registers with the screen position of the target and, if a match is found, the played has scored a direct hit.