IMU Calibration issue

[aknauer]

I take it this drift isn't in P-GPS mode? That would be odd. So I assume it is in Atti. You make an interesting point with regards to the FC being possibly slightly out of true when landing gear is raised.
Like you, I have designed and built many multi rotors from scratch and I have never been an 'IMU calibration junkie'. I prefer to get it right and then leave well alone unless mod values are out ocalibrated message presents itself.
I have not experienced any drift and have only calibrated with gear down and then only twice.....once the day I unboxed the Inspire and once more when I upgraded the FW to .17.
With regard to your drift problem, could you maybe shim the Inspire's legs in the opposite direction when you do the calibration. Only by a fraction (a few sheets of paper etc). The first time you do this will be a bit of trial an error until you get the shim value correct but then for future calibrations you will know what legs to shim and by how much?

Sorry for not responding earlier. Drift seems to be OK after new FW and re-calibration. It would still be nice to know where the actual reference level of the craft could be measured.