Abstract: An apparatus for accurately locating a stud concealed behind wallboard or the like includes a calibrated plate with an opening and an L-shaped probe having a coupling member on one end. A test hole is made in the wall and the probe is inserted through the hole until the coupling member goes into the plate opening. The probe is then swung through an angle from vertical until it strikes the stud. The plate has indicia to indicate distance to the stud, solving the right triangle of which the probe is the hypoteneuse.