So, the author's back-of-the-envelope calculation is 10%, yours is 13% (the average of 19% and 7.2%), and your conclusion is that "the author is just plain wrong"?
What would the author's rough estimates look like if they were "in excellent agreement" with yours? Would "11%" be close enough for you, or are you holding out for "12.8% to 13.3%"?
Can I suggest that you read the Wikipedia article on "orders of approximation"? Or, better yet, "Fermi problem"?
What would the author's rough estimates look like if they were "in excellent agreement" with yours? Would "11%" be close enough for you, or are you holding out for "12.8% to 13.3%"?
Can I suggest that you read the Wikipedia article on "orders of approximation"? Or, better yet, "Fermi problem"?
http://en.wikipedia.org/wiki/Orders_of_approximation
http://en.wikipedia.org/wiki/Fermi_problem