Are any calibrations kept when loading new firmware

I had some problems with my build, and I wanted to rule out the firmware by loading an older version. I also loaded arducopter onto the board and then loaded arduplane 3.7 back again.

Is the accelerometer calibration still stored on the board, or do I have to do the calibration again?

I don’t think recalibration is necessary unless stated in the release (I recall this happing once before). I’ve moved up from 3.2 all the way to 3.7 without recalibrations. The accelerometer offsets are all stored in the parameters, so as long as those are intact, it should be OK. This is why I’m careful to give my param file to someone else with the same airframe - they might no realise they’re getting my offsets as well!