Mathematical formula for the perfect head on a pint of Guinness

Lancaster, PA? Undisputed center of the Pennsylvania Dutch Country... large number of Amish farmers and Mennonites...etc. I really didn't realize that there was a bona fide Irish pub in the city. Oh well, perhapd there are a dozen or so Irishmen (and women who consume huge quanities of Guinness... and communicate their satisfaction. I'll be sure to stop in on my next excursion into the Keystone State.