A low-power electromagnetic digitizer table employing triangular-shaped electrodes arrayed in a single plane. A pointing device coil when energized induces signal voltages in the electrodes underneath. The electrodes are scanned in timed relation, and the induced voltages digitized and compared to determine...http://www.google.ca/patents/US4952757?utm_source=gb-gplus-sharePatent US4952757 - Low-power electromagnetic digitizer tablet
