A stud or joist sensor device and associated sensing method using a ratio of capacitance measurements from a plurality of capacitive sensing elements. The device locates a feature of an object or discontinuity behind a surface or wall, such as an edge and/or a center of a stud behind the surface, a joist...http://www.google.es/patents/US7116091?utm_source=gb-gplus-sharePatente US7116091 - Ratiometric stud sensing
