In a graphical display apparatus having a writing pad and a display device, X- and Y-coordinate position signals are generated by the writing pad to indicate the position of a pen on a work area on the data entry surface of the pad. A correction circuit formed by discrete components is operated in a...http://www.google.de/patents/US4737773?utm_source=gb-gplus-sharePatent US4737773 - Graphical display apparatus having a coordinate correction circuit
