answer: Mike explains to #Person1# what a nanometer is by making an analogy.
documents: #Person1#: Well, Mike, nowadays there's much talk about nanometer. But what on earth is it? 
  #Person2#: Nanometer is a length scale. It's one billionth of a meter, roughly ten times the size of an individual atom. 
  #Person1#: Hmm. . . it's hard to figure out the exact size, I'm afraid. 
  #Person2#: Well, let's make it this way. For comparison , 10 NM is 1000 times smaller than the diameter of a human hair. There are as many nanometers in an inch as there are inches in 400 miles. 
  #Person1#: I see. Thank you.