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.
Though the product is good, it was not useful to measure the angles of figures drawn as the middle circle is covering the picture. I was so disappointed that it could not be returned and it is of no use to me.... Waste of my money.