may receive signals from the light pens 20 a 20 b and 20 c each light pens 20 may detect light signals generated by one or more pixels making up the display screen 28 the optical transducers 34 convert those light signals into electrical signals and provide them to the video pass through box 38 in one embodiment the signals pass through the video pass through box 38 into a serial port such as a universal serial bus hub 50 coupled to the processor based system 39 the detectors 22 a c that detect the extension of the pens 20 with respect to the housing 18 may also generate signals in one embodiment the detectors 22 may be rheostats that generate a signal indicative of the extent of spring biased extension of the pens 20 from the housing 18 those analog signals may be converted to digital signals by the analog to digital converters 36 the digital signals may also pass through the pass through box 38 and the hub 50 to the processor based system 39 a detector 22 d may be associated with the portions 14 and 16 to determine their relative extension thus the detector 22 d determines the relative positions of the portions 14 and 16 which may be the result of the user pressing the element 10 into the screen 28 or releasing that force in one embodiment all of the detectors 22 may be rheostats finally user operation of.