models were in 2009 due to a software error that could cause improper calibration for AC electrical wires. Check your unit : Open the battery cover.

The Stanley FatMax Stud Finder 400 is a popular tool used for detecting studs and other objects behind walls. As a reliable and accurate device, it has become a staple in the toolkit of many professionals and DIY enthusiasts. In this essay, we will discuss the features, benefits, and usage of the Stanley FatMax Stud Finder 400, as outlined in its manual.

Don’t trust one pass. Slide left to right, mark the center. Then slide right to left. The center point should be identical. If not, recalibrate.

Stanley FatMax Stud Sensor 400 (Model 77-730) is an electronic stud finder designed to locate the center of wood and metal studs through up to 1-1/2 inches (38mm) of drywall. While "400" sometimes refers to the magnetic version (Model 47-400), the FatMax electronic series typically focuses on center-finding technology. Operating Instructions

Calibration is the most critical step for an accurate reading. If calibrated directly over a stud or dense material, the sensor will fail to provide a correct reading.

(Model 77-730) is an electronic tool designed to detect stud centers and live AC wires. You can access the official 77-730 FatMax Stud Sensor Instruction Manual for full details.

When the unit detects a stud, it will display its relative position. A "Center" icon and audible tone indicate the center of the stud. Use the built-in marking channel at the top of the unit to note the spot. Key Features & Specifications