I haven't specifically used an iDevice, but all the gyroscopes I'm familiar with provide the first derivative, not second. I'm also curious why he doesn't ment

I haven't specifically used an iDevice, but all the gyroscopes I'm familiar with provide the first derivative, not second. I'm also curious why he doesn't mention any use of magnetometers, which can give absolute orientation (not just the derivatives). Are the changes in position/elevation too large for airplanes to rely upon the local magnetic field of the earth?