21. The system used a light pen to draw on the screen of a 2250 Graphical Display Unit. 22. A light pen was provided as a pointing device, serving the function of the modern computer mouse. 23. This contains the horizontal color clock position when the light pen / light gun trigger is pressed. 24. See Lunar Lander for an example of a light pen in action on a vector graphics system. 25. Light pens were directly supported as well.26. Ivan Sutherland used a light pen in his programs as did Jack Gilmore and others before him. 27. Light pens and guns cannot be used on fixed-pixel displays because they have no electron beam to detect.28. Attorneys at the podium, or witnesses on the stand, can use light pens to " mark " exhibits. 29. Input was via a combination of light pen for pointing, and the PDP-1's front panel switches for commands. 30. In fact, all lightgun games for the XEGS could be played with the light pen and vice versa.
