There seems to be some argument about when to re-calibrate the compass.  The DJI Manual says to re-calibrate at each new flight location.  Some say to set it and forget it unless the app tells you to re-calibrate.

Could the source of confusion be that when they say "at each new flight location" they really mean a new locations that is very far from where it was originally calibrate, like hundreds of miles?

I guess one can argue, but what does it hurt to re-calibrate more often than necessary?  I suppose if you re-calibrate a lot you are increasing your chance of flying with a poor calibration if you calibrated around metal objects, on top of a parking garage, etc.

The DJI documentation is poorly worded or translated in a few parts, particularly compass calibration.
DJI have had ample opportunity to fix this and it seems they aren't going to.
There are many clever people flying Phantoms for a few years now and working things out much better than a you can from a couple of poorly written lines in the manual.
Read this to get an understanding of compass calibration, what it does and when it is necessary:
http://www.phantompilots.com/thr ... plete-primer.32829/

There are lots of confused ideas around compass calibration.
Most come from a lack of understanding of what compass calibration does.
Some people still believe that calibrating their compass sets the home point!
Others feel that calibrating the compass makes them safe ... so more calibration makes them even more safe.
This is using compass calibration as a superstitious ritual.

Unnecessary recalibration of a perfectly functioning compass introduces the risk of giving your compass a bad calibration when done in a magnetically distorted environment.
Here's an example of what can happen when you use the calibrate-every-time strategy:

You pretty much stated it all there in your post. Why redo a calibration if it's working good for you and risk missing it up. Labroides also stated it just right.

I think that one of the problems often encountered is that some people feel that they must calibrate before every flight because DJI said they should. The problem arises because those same people don't have clue about what constitutes a good place to calibrate. I always remember the classisc case of the guy who took his Phantom up on the roof of a multi-storey building, calibrated it right there amongst all the rebar on the concrete roof, took off and the aircraft flew in a circle and crashed into another building.

I don't calibrate on every flight. I use common sense by looking around at the environment.

Here is the logic...

When the phantom is on, it spends most of the time in the sky. When its high up, it has minimal magnetic interference/influence.
Users need to mimic the same conditions in the sky, but on the ground when calibrating. Hence all calibrations should be done at an open grassy field free of magnetic influence. Its best to find a field nearest to your flight location if you need to calibrate. Just use google maps.
The reason for the compass failures is that when the compass is calibrated near metal structures (rebar/buildings etc), it becomes influenced and a false "NORTH" is primed. When you take off and move further away higher into the sky, the magnetic influence is less and a the realistic north appears. This will now provide conflicting data to the fight controller and hence the P4/P3 will switch to ATTI to prevent fly-aways.

Compass is a very frustrating subject for me:
The P2 I had for a year before that I calibrated 90% of the starts - ZERO issues.
The P3P i now fly I try to leave alone as much as I can because: whenever I try to calibrate compass, it fails 3-7x before finally succeeding, IF it succeeds. Many times, it wont.
so day and night experiences.
and VERY frustrating. has kept me from taking off more than once.

Sebb Posted at 2016-9-27 20:59
Compass is a very frustrating subject for me:
The P2 I had for a year before that I calibrated 90%  ...

"whenever I try to calibrate compass, it fails 3-7x before finally succeeding, IF it succeeds. Many times, it wont. "

That usually indicates that you are trying to calibrate in a bad location.
Have you moved to a new area well away from magnetic influences?

labroides@yahoo Posted at 2016-9-27 14:01
"whenever I try to calibrate compass, it fails 3-7x before finally succeeding, IF it succeeds. Man ...

that surely was a factor in the beginning, and I am paying more attention to it. It has also had issues far away from any metal objects, e.g. a park.
but again: why is it 1000x more problematic than P2? zero problems vs. constant problems.

anyone know if it is a more sensitive sysytem now?
anyone can confirm same experiences comparing P2 with P3?

Sebb Posted at 2016-9-27 21:20
that surely was a factor in the beginning, and I am paying more attention to it. It has also had i ...

The P3 compass is not normally troublesome.
It may be that you have a bad one?

Hello , If you go to a new locations like hundreds of miles away, I'd suggest you to do the compass calibration.
And it's not hurt to calibrate the compass.

labroides@yahoo Posted at 2016-9-28 05:44
The P3 compass is not normally troublesome.
It may be that you have a bad one?

yea, pretty sure thats the case
well summer is over, i ll have some chance to send it in soon.

Agree...unless you travel a long distance, don't do it.  Just verify your IMU and Compass Sensors before each  flight.  Green = GOOD.

I normally see the Calibrate compass on the app and go from there.. which tends to be every new 1st flight i.e location.  If i land and change battery or stop for a break i wont re calibrate unless i have changed locations dramatically

I Agree with MGR57.
My reasoning is based on:
- Calibrating often will statistically introduce the risk of getting a bad calibration which could lead to a wayward aircraft if RTH initiates
- As long as your compass numbers are satisfactory (mod values between 1000-2000, I typically ensure mine are within 1400-1600), the compass is operating appropriately.
- Calibrating after traveling LONG distances should be completed to take into account changes in magnetic variation. (See attached isogonic line picture).

BTW I live in the US, that is why the picture is of the US.

simondobbins Posted at 2016-9-30 17:46
I normally see the Calibrate compass on the app and go from there.. which tends to be every new 1st  ...

If you get a Calibrate Compass message at new locations something is wrong.
The full message says something like Calibrate Compass or move to a new location.
This indicates that you areclose to steel or electric fields and the appropriate action is to move away from the magnetic distortion.
To recalibrate in a magnetically dirty area is asking for trouble.
If you have a good compass calibration and stay away from steel, you'll never see that message.
Are you perhaps trying to launch from reinforced concrete?