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.
Works perfectly. Definitely has made a huge difference to my weekly volleyball games. No one wants to play without this! Also, the other added benefit is less people ask to use the court you're on because having lines makes you look legit!