My guess is that the change in procedure is probably due to the concerns some have had about the gimbal while rotating nose down.
The purpose of the "dance" is to expose each of the three magnetometers to a wide range of magnetic values. After this the "gain" is set for each of the three magnetometers so that there will be a uniform response to the geomagnetic field. To determine what the gain needs to be each of the magnetometers needs to be exposed to a wide range of magnetic values.
After rotating 360 degrees in the XY plane the X and Y magnetometers have both seen positive and negative values. By orientating the AC so that the Z axis is now perpendicular to it's original orientation and then rotating the AC 360 degrees the Z axis sees the positive and negative values. The usual nose down (X axis down) brings the Z axis perpendicular to it's original orientation. But, so does side down (Y axis down).
The "dance" is just a procedure to insure that the three magnetometers have each been exposed to a wide range of values. It would work equally well if the AC were "tumbled" provided it was placed in enough different orientations. I once did an experiment where the calibration was done upside down. I.e., first rotation was done top side down and the second rotation was done nose up. Didn't make any difference.
The purpose of the "dance" is to expose each of the three magnetometers to a wide range of magnetic values. After this the "gain" is set for each of the three magnetometers so that there will be a uniform response to the geomagnetic field. To determine what the gain needs to be each of the magnetometers needs to be exposed to a wide range of magnetic values.
After rotating 360 degrees in the XY plane the X and Y magnetometers have both seen positive and negative values. By orientating the AC so that the Z axis is now perpendicular to it's original orientation and then rotating the AC 360 degrees the Z axis sees the positive and negative values. The usual nose down (X axis down) brings the Z axis perpendicular to it's original orientation. But, so does side down (Y axis down).
The "dance" is just a procedure to insure that the three magnetometers have each been exposed to a wide range of values. It would work equally well if the AC were "tumbled" provided it was placed in enough different orientations. I once did an experiment where the calibration was done upside down. I.e., first rotation was done top side down and the second rotation was done nose up. Didn't make any difference.
