I agree, if I'm within eye distance from where I calibrated, I do not recalibrate, but anything farther, I always recalibrate ( a) better safe than sorry , ( b ) you never know if you had some mAgnetic interference, on the way to fly zone ( buried wire,speaker magnet ( in car on ride over ), or other UNKNOWN factor? Truth is you could calibrate after each flight ( not necessary ) but doesn't hurt anything to do. This brings me back to ( a ) better safe than sorry ! I personally recalibrate after 5 full batteries spent, even if in same location, and I use line of sight method ( if I cannot physically see ( with my eyes ) my last fly location, I recalibrate! I have never had an issue ( yet ). It is personal preference for the most part.
Most people recalibrate at each new location ( regardless he distance ? )
I believe the new 3.0 firmware with newest assistant software. Has the ability to tell you if your compass
Is out of whack? Pretty cool feature. I personally have not tried yet, but might check it out later.
Take care my friend,
And I would not worry to much, just keep a close eye on your phantom ( right after take-off ) if it does small circles, or tries to fly away from you at an angle ( ie: forward & left / backwards & right / ect, ) that is the first sign of compass mishap. Land right away, and recalibrate ( also take our time during calibration ) it is not a race, take it steady and slow the phantom will wait for you, you have plenty of time to complete accurate calibration!
Jerry D
USA
( J Dot )