Why does my StudSensor™ show a wide "center" of a stud instead of a single point? Why are the "edges" 3 inches or more apart?
You're most likely over a double or triple stud. Double and triple studs (triple studs are much rarer) are installed around doors, windows, or anywhere the builder thought extra support was needed. Your tool's center-finding feature may detect a wide center zone rather than the center of double studs, but the edge finding capabilities will be unaffected.
Don't nail, drill, or screw anything into the center of a double stud — anchoring something between the beams won't give you the support of a normal stud center. If you need to attach something to a double stud, either use two screws or nails side-by-side for extra support, or find the center of one of the studs. To do that, use the edge-finding features and determine both outside edges of the double. Then measure in 3/4" inwards on either side (assuming your studs are the standard inch and a half wide) so you can target the center of one of the studs. While it's safe to nail/anchor into the center of triple studs, make sure you use the edge finding feature over a wide range so you know absolutely where that center is.
If your scanner has a metal scan feature, or if you have a dedicated metal scanner, scan the area for metal pipes. A metal pipe can be directly attached to the side of a stud. If the pipe is close to, or up against the back of the dryway or wall board, it can appear as a stud edge to the scanner. A metal scanner or the metal scan feature on a Zircon® MultiScanner® will alert you to the presence of the pipe.
If the wide center is accompanied by a WireWarning® detection there may be a live electrical line (Romex) running up the side of the stud, or running through the center of the stud in close proximity.