The beam pen: a novel high-speed, input/output device for cathode-ray-tube display systems

In recent years there has been considerable interest in providing rapid communications between a man and a computer. A most useful communication system in this regard is a cathode ray tube (CRT) computer display and a hand-held "light pen" to report to the computer whenever a lighted spot on the CRT display falls within its small field of view. The pen may be used to identify or select a particular displayed item which the man wishes to call to the attention of the computer. Also, a feedback loop may be programmed to keep a displayed pattern of spots centered in the pen's field of view. With such a loop the displayed pattern follows the moving pen, and the system becomes a very versatile graphical input device. This process is known as "pen tracking."