Doug the myzipcode cookie is good for one browser session meaning you must close the browser and reopen if you want to enter a new zipcode
( Bel Air,Maryland )
Thats what I see because my zipcode is 21009 so your calculations are correct for US.
I would suspect whatever source code the initial user got he my mistake mixmatched the columns as I posted a few posts ago. I beleive he even confirmed this in his old thread and even here. The calculations are only as good as the data entered. This was a hand made cvs from my understanding.