Hello, I was viewing a lecture of one of the professor's most possibly in MIT who demonstrated in the class room, by calling a boy and measuring him, while standing, a certain measurement say 5 ft. After that he asked the boy to lie down and again measured him and found that there is a difference, say +- some amount. He concluded that there is always a uncertainty in measurement while standing and the same person lying down. Can anybody please explain me the reason? Why? Thanks.