Instead of speeling it out here, I'm going to refer you to the
alt.smokers.cigar FAQ, if only to avoid starting a battle royale with the heartfelt-but-scientifically-challenged.
There's a ton of questionable info on the WWW. I find that the ASC FAQ is reliable, and they refer you to the scientific derivations, if, like me, you want to check it out yourself. Many websites/stores have some prominent misconceptions posted.