How to Tell a Billion From a Million

John Lanchester, in his review of "Lords of Finance" in The New Yorker:

Try the following thought experiment, suggested by the mathematician John Allen Paulos, in his book “Innumeracy”: Without doing the calculation, guess how long a million seconds is. Now try to guess the same for a billion seconds. Ready? A million seconds is less than twelve days; a billion is almost thirty-two years.