Be gentle 
, edited in LumaFusion on my iPad.
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Blimey! I am surprised!
I wonder if the Air has a less sensitive / more accurate compass?
I didnāt even consider compass issues, what could have happened?
Iāve never had an issue - in 4 years of P2/MP ownership - beyond a message (MP) or relevant flashing LEDs (P2) - that told me it was upset and wouldnāt let me take off, anyway.
In each case, it was (after the warning) rather obvious why ā¦ heavily reinforced concrete in the ground (Southampton docks), reinforced trig point (annoying that one - LONG grass everywhere and it was the only exposed flat area), etc.
I tend to work on the basis that if itās happy to take off - then thereās no issue.
In fact ā¦ Iāve only done a compass recalibration twice ā¦ and that was on the P2 going to Sardinia and on the return.
Last year I drove 8,000 miles from the UK and all around Italy and, in the 18 months Iāve had the MP Iāve never done one once. Never had a problem. People worry too much ā¦ IMO.
Edit: I would add that my travels have been in southern Europe ā¦ I would suggest itās more relevant for travelling further afield.
Whatās relevant is local magnetic variation, and some parts of the world have a far greater variation than SW Europe.
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Excellent info Dave 
I wonder what happens if you fly here ā¦
Your drone will RTH to the core of the sun 
Iāve flown a few feet over large steel structures. What I noticed was it does not hover dead on the spot, it hovers in a circular motion. Not an issue if your above the object but could be problematic if in tight quarters.
I fancy flying out from the Isle of Wight to The Needles Lighthouse ā¦ and landing on the helipad on the top ā¦ which is made of sheet steel. 
I āthinkā I might have problems taking off again.
I must try this on some other, slightly more accessible, sheet of steel before I try the real thing.
ā'Scuse me, Mr Trinity House, can I have my drone back?ā might not cut the mustard. 
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Iāve had to recalibrate both times Iāve taken the Mavic Pro on holiday (Ethiopia and South Africa). Wonder if itās distance related, or hemisphere change related? I realise Ethiopia is still north of the Equator, but itās sort of close
Anyway, the check list screen on power on wanted me to calibrate.
As I mentioned elsewhere, Iāve had volcanic rock cause magnetic interference, such that no amount of waving the Mavic about was going to help, it just refused point blank to fly, with all sorts of red error screens (should have taken some screen shots I guess)
See the map above ā¦ the bigger the change in magnetic declination, the greater the chance you need to recalibrate.
The lines on that map show points of the same declination.
I should read, shouldnāt I?
Interestingly, though, when I got home it didnāt prompt me to recalibrate. Does it remember? I did, though - seemed safest, though Iām normally in the ādonāt fiddleā camp as well
The fact that points have the same declination doesnāt mean there wonāt be other reasons the MP throws a magnetic wobbly ā¦ but does mean that declination wonāt be a reason.
Iāve seen people recalibrate ābecause something metallic was closeā. To my way of thinking, this is not a reason. Whatās important is that itās correctly calibrated for when itās in the air, flying, at distance from the offending object, so not a reason to recalibrate ā¦ IMHO.
Following up on this, and my thoughts about flying to The Needles Lighthouse ā¦ I just took off (away from), then landed on this 10ton rated manhole cover ā¦ then took off again.
No problems.
I also tried rebooting and starting from the manhole cover.
No problems.
Shows how difficult it is to predict the MPs response to such things.
It also means Iāve not decided itās OK to fly to the lighthouse. I need to test from something it really wonāt take-off from after booting, then see if I can āvisitā it and take off.
Dave, Iām surprised you managed to take off from that.
Last time I was out, we were flying from a hill out on moors. One patch around a square meter would give a compass error on mavic, a P4 and P4P.
A gauss meter app I had on phone was also off the scale when held to that point.
Iām half tempted to go back with a spade and see whatās causing it.
The other issue you have with landing somewhere mid flight is it resets the homepoint. You would have to manually set it to device after takeoff otherwise it would be heading back to lighthouse if you lost signal.
Iāll just have to not lose signal!
It would be a bummer if I lost signal WHILST it was landed! #Hmmmmmmm LOL!
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I was less that 2ft from 2.5 tons of Shogun, too. LOL!
It does object ā¦ sometimes. Southampton docks was one such time ā¦ so I know itās actually working, in this respect.
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I was about to try something else ā¦ and take the video proof ā¦ but itās now raining a lot more than when I was out there testing before. Iāll do one, tho.