There is a factor of +1 missing from both terms resulting in a negligible calculation error. The section has been re-written as follows: <img width="695" alt="Screenshot 2023-08-06 at 08 21 21" src="https://github.com/attack68/book_irds3/assets/24256554/a7cd2cbf-5462-4f9a-8a90-27d7758ad6fe">