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 analyzes reviews to verify trustworthiness.
The only issue is, it is already out of date and many of the examples don't work. Just a warning in case you are not able to troubleshoot. Most of the stuff I was able to figure out, but it can be intimidating for the new user.