People that use laptops to connect to their Phantoms and do Calibrations to the IMU. Laptops like newer apple laptops have rare earth magnets in the screen to do two things. First to hold the screen closed. Second to put the laptop to sleep. Or let the system know that the laptop is closed. So I would recommend that you use at least a 6 foot usb cable to do the calibrations to to the IMU. You can check this by one of two ways. The easiest is to use a paperclip around the edges of the laptop screen and see if it sticks. On my MacBook Air 13in mid 2013 I found four spots on the front that a paper clip sticks firmly and 3 on the back of the screen, not as strong but sting enough toehold the paperclip to it. The second way is to use a actual needle compass and see if moving it around the screen of your laptop makes it deflect. Now I know that after you do the IMU cal that you should do a compass calibration out doors away from metal or other sources of magnetic interference. Even overhead power lines can be a problem.