To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyses reviews to verify trustworthiness.
The author starts with a number of standard drawing exercises and then shows how he makes a drawing. His portrait section is just one completed drawing after another. The only thing we find out is the person he has drawn. He never mentions standard proportions.