Abstract: An improvement in a magnetic tape playback apparatus for determining the location of any portion of the magnetic tape as it passes the tape reading head including optically readable indicia means printed on the magnetic tape representing encoded information and means for optically reading the indicia including a light source and detector both mounted on one side of the tape. The improvement is compatible with existing magnetic tape playback devices and magnetic tape cassettes.

Abstract: An automatically compensated light pen for use with a video display monitor incorporating a cathode ray tube, including, a detector for detecting light pulses produced by the cathode ray tube when the detector is positioned adjacent the cathode ray tube at a particular desired location and for producing electrical pulses in accordance with the light pulses, a variable attenuator having a first input coupled to the output of the detector and responsive to the electrical pulses from the detector for producing variably attenuated electrical pulses and having a second control input responsive to a control signal for controlling the level of the variably attenuated electrical pulses, a threshold comparator coupled to the output of the variable attenuator and responsive to the variably attenuated electrical pulses for producing output electrical pulses when the level of the variably attenuated electrical pulses are higher than a particular threshold level for the threshold comparator, and a peak detector coupled be