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.
Don't buy on Kindle if you can't see well! Although the book is good, the kindle version is not good at all. I use kindle as it's great for visual impairment, but if you up the font-size on this one, half the copy disappears off the side of the screen. Bad design.