Suddenly different compass offsets after calibration

Hello, I have been flying arducopter for 3 months now and I have been a little surprised that the copter is very stable with the quite old 3.2.1 firmware, but one thing that has been very annoying is that I need to recalibrate the compass almost every week I fly. Is it normal?

But another issue that has been disturbing me lately is that this Sunday I wanted to fly in a different location, I flew there before, and calibrated the compass there before too but this time when I calibrated the compass the offsets were much different from normal (my normal offsets are around [-210, 15, 50]), but this time they were very close to 0 on all axis, maximum 10! Is that normal? The copter flew fine like always but after looking at the logs I noticed many compass / magnetic field interference issues, I also needed to calibrate it twice before it succeeding!

Also note that this happened the same day the world changed time, idk if that matters just pointing out.
I will fly tomorrow and calibrate it again in another location close to where I live and see the offsets!

Compass calibration is performed to record offsets from on-vehicle anomalies not for geographic location. There is no reason whatsoever to re-calibrate the compass(s) due to a change in location. The only reason to re-calibrate the compass is if there is a hardware change on the craft. And don’t confuse declination with correction offsets. They are 2 different things.

What do you see here as the 1st Tip in the Wiki?
https://ardupilot.org/copter/docs/common-compass-calibration-in-mission-planner.html

Then why is it that often I encounter toiletbowling, but after re-calibrating it goes away?

Because something changed in the vehicle without you noticing it. How well is that compass attached to the vehicle? Can it rotate?

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The compass is external with GPS attached on a stand, it can’t move at all. But remember that I use arducopter 3.2.1, does that version have the world magnetic model?

I think it has a simplified version of it, yes.

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