In Go, rank indicates a player's skill in the game. Traditionally, ranks are measured using kyu and dan grades, a system which also has been adopted by many martial arts. More recently, mathematical rating systems similar to the Elo rating system have been introduced.? Such rating systems often provide a mechanism for converting a rating to a kyu or dan grade.? Kyu grades (abbreviated k) are considered student grades and decrease as playing level increases, meaning 1st kyu is the strongest available kyu grade. Dan grades (abbreviated d) are considered master grades, and increase from 1st dan to 7th dan. First dan equals a black belt in eastern martial arts using this system. Top players can attain a professional dan grade (abbreviated p), with the very best reaching 9th dan professional. The difference among each amateur rank is one handicap stone. For the professional ranks, the difference is roughly one handicap stone for every three ranks. For example, if a 5k plays a game with a 1k, the 5k would need a handicap of four stones to even the odds. Top-level amateur players sometimes defeat professionals in tournament play.The rank system comprises, from the lowest to highest ranks:

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