The question was why mass and energy should ever be related at all, and why c² turned out to be the relationship between them. By minimizing the meaning of c² - reducing this to a "units conversion", that relationship remains obscured. This is why you can't call it a conversion factor. You'll never get the point. As opposed to . . . understanding received on another world . . . perchance the planet Remulak? :bugeye: Which ratio? :yawn: And where does that lead you?