A dual sensitivity stud sensor senses studs through both thick and thin surfaces. Studs are sensed by detecting a change in the capacitive loading of plates as they are moved along a surface and into proximity with a stud. The sensor informs the operator when the sensor has (incorrectly) been calibrated...http://www.google.es/patents/US6023159?utm_source=gb-gplus-sharePatente US6023159 - Stud sensor with dual sensitivity
