Simone Biles is probably the best gymnast in history. But even if she wins gold at the Rio Olympics, the 19-year-old American is very unlikely to earn a perfect score, as her predecessors Nadia Comaneci and Mary Lou Retton did.
Gymnastics’ new scoring system, implemented in 2006, is designed to evaluate both difficulty and execution. Though the judging often confuses fans, it’s not that hard to understand once you know the rules. In the video above, Dvora Meyers—the author of the new book The End of the Perfect 10: The Making and Breaking of Gymnastics’ Top Score—From Nadia to Now—explains how gymnastics scoring changed, and why the “perfect 10” is a thing of the past.