I was thinking... now that we have got a god bunch of PDAs using Linux (discard Nokia 770, which hasn't got a IR port) Can we use the IR diode in the box to emulate an old fashionated Light Pen? I mean, is it fast enough to detect the CRT scan? It could be sincronised by averaging or some clever trick so it does not need to read the crt sync signals, or lacking this it could receive them via USB, timestamped.