Wow, I feel like I've contributed something here. I started a long running thread that didn't involve the 4th of July or gun control! Ok, forget the dry humor. Thank you all, now I know more about light pens than I would have imagined possible. The $65536 question now is, how do I get a hold of one? I'd like to try it on my 6845 video controller based machine (PCjr CGA). I'm willing to learn to solder if necessary. :-)