I installed
Teslameter too. While the app seems to work just fine, I'm not sure exactly how to know how strong of a magnetic field it takes to negatively affect the Mavic compass. With some experimenting, I suppose you could figure that out.
There's an easier way to do this without using that app. Set your Mavic on the ground, power it up, and watch the red aircraft symbol on the map in DJI GO
(or the attitude indicator at the bottom, left of DJI GO if you cannot see the map). If the red aircraft symbol is pointing in the wrong direction or it's rotating very slowly, then the Mavic's compass is likely being affected by a nearby magnetic metal object.
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