acceptable mag_field and compass offsets?

Hi all, can someone confirm what acceptable compass offsets and mag_field are?

I've been trying to improve my compass accuracy lately (3DR Quad C), and had a bit of a win today by raising the APM platform higher to get away from the battery wires connecting to the power distribution board immediately under it. This seems to have improved things a lot, the COMPAS_OFS_Z value halved:

Was:

COMPASS_OFS_X,13.712
COMPASS_OFS_Y,96.453
COMPASS_OFS_Z,-411.979

Now:

COMPASS_OFS_X,21.238
COMPASS_OFS_Y,135.396
COMPASS_OFS_Z,-191.489

And here's a graph of mag_field versus throttle from a flight today. I can't find the info about what is acceptable, I had the figure of 150 in the back of my mind, so I'm guessing that's a delta of 150 from the baseline (i.e, with throttle off)? In which case the graph below is within that threshold - how does it look?

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  • Just tying this up with some info on max mag offsets. Apparently -150 to 150 is good (from Randy on the dev call)

  • BTW, I did some pretty accurate auto flights today, there was a slight deviation after each waypoint but once it was established en-route between waypoints it's very close to the tracks.

    Another auto mission was to stay in one location and use CONDITION_YAW to point to each point of the compass in turn with delays in between, and it did a great job of that too.

    However, I notice when I'm on the ground connected to the Mission Planner, the direction it shows is up to 90 degrees off from the heading I know it to be pointing in. Is this because it has the compass calibrated to flight conditions with the motors running, so when they're idle it's out of whack?

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