The (often referred to interchangeably with the S300 or related multi-depth models) is designed to locate the center of wood and metal studs through various wall thicknesses. Quick Setup & Calibration
If you start the calibration directly over a stud, the device will "auto-zero" incorrectly. It will then beep everywhere except the stud. If you suspect a mistake, lift the device, move it 12 inches to the left or right, and repeat. stanley fatmax stud finder 400 manual verified