Oops, you're right, I got the \pi in the wrong side of the equation! Evidently this is called Duff's Rule (http://www.johndcook.com/blog/2009/07/01/three-rules

Oops, you're right, I got the \pi in the wrong side of the equation! Evidently this is called Duff's Rule (http://www.johndcook.com/blog/2009/07/01/three-rules-of-thumb/ http://www.johndcook.com/blog/2009/07/01/three-rules-of-thum...).