Stud Sensor Pro SL expands on the features of Stud Sensor SL adding Deep Scan mode to scan thicker wall surfaces The Stud Sensor Pro SL stud finder has all the great features of Stud Sensor SL model plus patented Deep Scan technology to reach depths up to 38 mm Its the sure way to find the edges of wood & metal studs to securely hang pictures shelves mirrors & more Standard scanning mode locates the edge of wood or metal studs behind most common nonmetallic interior surfaces up to 19 mm thick Deep Scan mode doubles the scanning depth to 38 mm A red LED lights up every time a stud edge is approached Patented Spot Lite Pointing System & green LED signals when the stud edge is reached Should scanning begin over a stud Zircons patented overthestud indicator alerts the user to start the scan in a new location Patented Tru Cal technology calibrates to any walls density & a green LED Tru Cal light alerts the user when the tool is ready & calibrated