There are various systems of Go ranks and ratings that measure the skill in the traditional board game Go.
This system is also commonly used in many East Asian martial arts, where it often corresponds with a belt color.
[5] The system was later used in martial arts schools; and is thought to be derived originally from court ranks in China.
This means that players will have to show good results in tournaments or pass exams to be awarded a dan rank.
In Japan and China, some players are awarded an amateur 8th dan rank as an honorary title for exceptional achievement.
In the United States, amateur dan ranks are often based on the AGA rating system.
Similarly, some players have achieved 9th dan amateur ranks in the rating system of online Go servers.
The difference between these grades is much smaller than with amateurs however, and is not based on the number of handicap stones required.
This is done by varying some of the components of the Elo formula to achieve a close match to the adjacent table.
However, there is a slight inflationary mechanism built into the ratings adjustment after each game to compensate for the fact that newcomers usually bring fewer ELO points into the pool than they take out with them when they cease active play.
This involves more intense computation than other methods, but is claimed that "in comparison to Elo, Glicko, TrueSkill, and decayed-history algorithms, WHR produces better predictions.".
[7][8] The website Go Ratings implements the WHR method to calculate global player rankings.
[9] In a small club, ranks may be decided informally and adjusted manually when players consistently win or lose.
Player pools that do not regularly mix (such as different countries, or sub-groups on online servers) often result in divergent playing strengths compared to the same nominal rank level of other groups.
This probability depends only on the difference between the two players' ratings, but its magnitude varies greatly from one implementation to another.