From a similar thread.....

I fully agree with what labroides is saying, when i got my P4, i did go through a similar dilemma, read the link supplied above and on other foums too on the compass dance.

I recently did a trans-siberian train trip and took the P4 along with me,

Calibrated in Lake Baikal in Russia, an open water area, no interference, and then flew it in Mongolia - 800Kms away, then flew it in the Great wall section in Beijing - around 1300kms + 800kms away from calibrated point

No where else did i do the compass dance other than the first time, every other time, i lifted it up in the air, hover for 5 to 10 secs to see if all is well and all was well, no issues.

So the main point is that once you have a good calibration, you don't have to do it again (even dji wont vouch for it, nor will they support it if something goes wrong), by calibrating every time you fly, you increase the possibility of getting a bad calibration than making it any better.

Adam Flurk Posted at 2016-8-26 11:01
Your car has a compass?

Two of my cars have a compass. Many do for the last 10 years, some since the 90's.

Snowwolfwarrior Posted at 2016-8-25 19:39
I'm the same as Wmichaels1 I have one field that is in middle of nowhere that I just use to calibrat ...

WOW you have flew 200 miles, you must have a big battery