A four-quadrant multiprobe edge sensor system which comprises a printed circuit board having a plurality of data probes mounted thereon which include four data-detector probes particularly-positioned. The data-detector probes include a support body, and an arm supported by the body and attached thereto...http://www.google.co.uk/patents/US4219771?utm_source=gb-gplus-sharePatent US4219771 - Four-quadrant, multiprobe-edge sensor for semiconductor wafer probing
