After nearly a year of flying quite often, usually within 50 miles of home, my Phantom would not track a straight line yesterday.  So, I calibrated the compass and everything was fine after that.  The last calibration lasted nearly a year with no issues.  I live in a remote area, and the places I fly are also not developed at all, so I don't get much in the way of electromagnetic interference.  Still, I thought it was a remarkable stretch of time to go without calibration.  In addition, I have not needed to calibrated the IMU in probably 6 or 8 months.  I expect others will have different results, but this illustrates what is possible.  I have had that particular Phantom for 2 years, so it is getting a bit aged.  I'm still quite happy with it.

Thanks for sharing with us your experience. Wish you have a great time on flying the drone.

Normally I only recalibrate my compass after firmware updates.

I like to do the IMU and Gimbal first, then take the drone out of doors and do the compass drone dance.

I haven't traveled with my drone, over two hundred kilometers from home, to let that be of a calibration concern, otherwise.


RedHotPoker

Are you sure that you didn't take off from near some iron yesterday?
Or maybe the aircraft has been modified or repaired before yesterdays flight?
Or maybe the aircraft has been near some big magnets?

A perfect example of why sometimes less is better.