I think paul bucheit's post http://paulbuchheit.blogspot.com/2007/03/equity-math-for-startups.html http://paulbuchheit.blogspot.com/2007/03/equity-math-for-star

I think paul bucheit's post http://paulbuchheit.blogspot.com/2007/03/equity-math-for-startups.html http://paulbuchheit.blogspot.com/2007/03/equity-math-for-startups.html is a much more clear explaination of the same concepts.