Then let me add another bit of 411... at my location there's metal & power all around me within 8' of the landing zone. Why would I attempt to calibrate an otherwise happy compass of a PV or 777 when it flies perfectly stable, and risk throwing it out of whack just for the sake of performing an unnecessary gratuitous calibration for no logical reason. But I'm open minded, give me a logical reason and I'll do it. This forum is full of posts of folks who have done so resulting in worse performance than when they started. Of course, being aware of & moving away from metal, magnetic fields, and power lines before attempting such recalibration would probably have saved them from that, but oh well. If I got an error message or experienced a flight anomaly from where I took off, then recalibration is one of the first things I'd consider.
iDrone