I just bought a new P4, run some tests, and updated the firmware for the bird and for the RC. I'm hoping to take it out for a spin tomorrow. I read the manual cover-to-cover, but not once did I encounter any mention about IMU calibration which used to be a big deal with the P3.

I know that I have to do a compass calibration, but what's DJI's official stance on IMU Calibration? Should I do it after every firmware upgrade? Or with every compass calibration, or should it only be done when the DJI Go app tells me to?

Also, I've noticed that in the specs for the P4 they talk about how the P4 has redundant IMUs. Does this mean that I don't have to calibrate it as much? I'm new to the phantom series and the P4 is my first bird -- I'm trying to be super diligent and careful so that I don't crash a $1400 drone, but I'd appreciate a response from any pros here.

Yeah, don't overdo the compass calibration either, once you get a good one, leave it alone. Lots of people get into trouble by over-calibrating things more than is necessary.

Don't think DJI corporate has an "official" policy on IMU calibration. At least one DJI forum poster - DJI-Ken - a good guy, who is very knowledgeable and helpful, recommends calibrating the IMU after every firmware update. I resisted at first on my P4, because it was working fine with very level camera horizons and rock stable hovers.  However, after one rough flight with unplanned acrobatics (another story), I decided I better calibrate IMUs in P4 before flying again.

I was pleased to find that I did NOT have to chill the P4 before calibrating the IMUs.  On the P3Pro, if you recall, it is necessary to chill the aircraft in your refrigerator or by holding it in front of car's A/C vents prior to IMU calibration to avoid substantial/annoying "IMU is warming up" delays on subsequent first flights of the day following IMU calibration.

Just be sure to place your P4 on a level surface (use a bubble level to make sure) before beginning the IMU calibration. It's pretty painless and there is no obnoxious beeping while the calibration proceeds.  Took about 5 minutes, if I recall correctly. Message said it might take 10 minutes.

I'll probably follow DJI-Ken's advice and calibrate IMUs after every firmware update.

Thanks guys! Well I did do the firmware upgrade, so I will do the IMU Calibration along with a compass calibration before I take her out to fly tomorrow. Thanks again for your help!

You have to calibrate IMU after long transportation and after every firmware upgrade to guarantee the stable flight

Thanks Tim! Much appreciated