Amazon calculates a product's star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers and factors that establish reviewer trustworthiness.
Its very useful and handy. Besides its painless. Regular threads for upperlips used to bring tears in my eyes. I am wondering why I didn't purchase it earlier :) However its not very suitable for eye brows as you have to be very precise and accurate. This is good for upperlips, chin etc.