It works wonderfully if you keep this in mind

1st of all, its important to know that your iPhone (6s) is detecting metal at the very top middle of the phone, next to the camera flash.
2nd, its important to mark several screws/nails up and down the stub. That way, you can get a better idea of where youre going to nail your frame of whatever.
3rd, your studs are going to be 16 inches apart. That should also help with placement.

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