I could use some advice on using a Zircon MT7 metal scanner for a wind mitigation inspection on a house with a metal roof. I’m trying to locate nails in the rafters, but I’m having trouble because the scanner keeps picking up the metal roof instead. I’ve recalibrated multiple times, but it still won’t focus on the nails, only the roof. Has anyone dealt with this issue before, or have tips to improve accuracy?
Welcome Robert! Not familiar with the metal scanner you reference, but it would make sense that it’s going to pick up the highest density of metal in the area. Plus, I hope you are looking for screws and not nails. Metal roofs are not nailed down or at least they shouldn’t be.
I’ve always used a zircon M40.
Then you can pinpoint it about an inch lower to make your marks.
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I guess that goes back to his question on why is picking up the metal roof instead? Hopefully you can help him with because I know I can’t. 
Yes, the metal roof is screwed to the deck. I am trying to find the nails that attach the decking to the rafters.
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Makes more sense now. Maybe Marc will pipe in again to explain how he does it.
You obviously have no clue on this subject.
The MT7 is too fat/wide, what I suggested will pinpoint the fasteners.
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I have the MT-6. When I have a metal roof or truss plates around, I just wave it quickly. It’s not an exact science. Might take some waving back and forth to nail down the nail.
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MT6 is what I used to use. Like Marc said, hold it down from the deck slightly to detect the nails away from the metal roof covering.
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As said earlier. DH! 