A coordinate-capturing apparatus suitable for inputting handwritten characters or diagrams to a computer or a printer is disclosed. The apparatus includes an ultrasonic transmitter mounted on an input pen for transmitting ultrasonic waves, two ultrasonic receivers for receiving ultrasonic waves transmitted...http://www.google.es/patents/US20010020936?utm_source=gb-gplus-sharePatente US20010020936 - Coordinate-capturing apparatus
