Guitar Fretboard Radii explained

In response to a question from JaffCox 8993, I'm attempting to understand and explain this aspect of guitar design. Not to be confused with the various shapes of the necks, i.e., the part that sits in the palm of your hand. NOTE : Regarding C.F. Martin guitars: Apparently, I have given incorrect Information regarding the fretboard profiles of their guitars, which I have said 12" which I arrived at by perusing their very complex marketing website. I now believe this to be incorrect and that they generally use a 16" profile. My apologies.