No one is disputing that VARIATION can be ignored. What you don't understand is that VARIATION isn't determined during the compass calibration. VARIATION determined at the beginning of the flight after the GPS coords are known.
Where do you get this from ... I have NEVER said that Compass Calibration determines Variation.
What I said is that the lines of flux of Variation crossing the lines of flux of the AC's deviation when AC is rotated causes a changing vector result ..... THAT is what the 'dance' is for !! To calibrate to compensate for the VECTOR results !!
Compensating for magnetic effects that don't rotate with the AC is mathematically impossible. If you know how this could be done then I urge you to publish your idea. You'll be famous.
Please keep it sensible ... as I keep saying .... the ROTATION of your AC causes VECTOR changes in the interaction of the external Variation and on-board Deviation ...
Even that bastion (Wikipedia) of the uneducated states clearly :
"Solid state compasses :
Small compasses found in clocks, mobile phones, and other electronic devices are solid-state microelectromechanical systems (MEMS) compasses, usually built out of two or three magnetic field sensors that provide data for a microprocessor. Often, the device is a discrete component which outputs either a digital or analog signal proportional to its orientation. This signal is interpreted by a controller or microprocessor and either used internally, or sent to a display unit. The sensor uses highly calibrated internal electronics to measure the response of the device to the Earth's magnetic field."
And, please, it's not necessary to explain that external and on board magnetic effects are combined and the magnetometers can't separate them. This is a well understood concept and we are aware of it's implications.
So why do you ignore it in your 'AC rotation' claims ?
Finally, your comment about it not being necessary to look at possible bad-calibration-causes-incident scenarios says a lot. Basically, what you're saying is that you don't need to look at evidence because you know it's true. When I see these posts it's always something like we know it was caused by a bad calibration because that's what causes these incidents. There is never any attempt at evidence based analysis. It's a text book example of confirmation bias and your description of the incident you witnessed is a good example. By your description it's also possible that the cause was just that the launch site was geomagnetically distorted and the calibration was not flawed.
Again - you are twisting words ... calibration is not 'flawed' - it is what it is ... If there is unusual magnetic influences when the guy calibrates - as long as the results lie with the programmed limitations - it will accept. It is not 'flawed' - it has an error in it that is allowing for that local anomaly. When the AC leaves that location or the effects of that anomaly - the calibration then is out of synch with its situation.
Let me ask a question then :
If calibration as you suggest is not influenced by external unusual magnetic effects - why is it advised by all and his dog to calibrate in a clean area away from local influences such as iron work, pipes, cables, metal objects... even down to not having your mobile or other gear nearby ?
Sorry but calibration is a serious matter and needs care. To 99.9999% of users - they don't care what or why ... they just want to calibrate and fly ...
Nigel