Long time ago I wrote a documentation for ImageCalibration as a pidoc. For some reason it was never integrated in the release (it is possible that it contains error or my english is too bad). It seems that the process did not change that much, so I uploaded it in a cloned repository of Reference-documentation:
https://gitlab.com/bitli/Reference-Documentation, it is under tools/ImageCalibration.
Maybe somebody could check it and possibly correct it so that it could be included in the official release, if Juan is interested.
I have attached a PDF printout of the generated page.