A term applied by Western Union Telegraph Company to teletypewriters that are not part of a multiplex system. They usually provided fOR alternate transmission in both directions. If wORking simplexORhalf-duplex, what was keyed in at the keyboard would be typed out at the printing pORtion. If wORking full-duplex, sending would be blind as the printing pORtion was being used only fOR reception. (2000-04-02)