Here is the ITD guide covering common questions about tournament pairings.
This is a pairing system developed in the UK to match contestants against others of the same McMahon Score as far as possible. A player's McMahon score starts at their entry grade and gets better by one point for each game won. A 4 kyu with two wins is on the same McMahon score as a 2 kyu with no win. The player with the best McMahon Score at the end of the tournament is the winner. Note the system used to be called "MacMahon" and is still called that by some.
The top dan players all start on the same McMahon Score. In a three round tournament the number starting on the bar should be no higher than eight, so that there can be a unique winner. Lower players can meet players above the Bar if they win sufficient games.
This is when you play someone whose McMahon Score is different from yours. This usually happens when there is an odd number of players on the same McMahon Score. The number of drawn up and drawn games you play is normally minimised.
The McMahon draw endeavours to gave a player a balance between playing black and white. If the balance is even, a random choice is made to decide black and white, even if one player is lower graded or has been drawn up.
A McMahon draw tries to maximise the number of even games played. A handicap of "no komi" is given if the McMahon Score difference is two. Handicap stones are given if the difference is three or more. These handicaps are based on one less than the McMahon Score difference. So a 20 kyu on zero wins will play an 18 kyu on two wins with a three stone handicap. Often there are insufficient players in the bottom part of the draw to give any even games. No handicap games are played above the bar.
The draw tries to keep players from the same club apart, to avoid someone travelling 100 miles only to play the people travelled with. However often there are insufficient players on a particular score who are not from the same club, so same-club games cannot be avoided. Sometimes clubs are ignored when pairing players above the bar.
After name, club and grade, the middle columns give the player number of each opponent followed by "+" for a win, "-" for a loss and "=" for a jigo. Then come various columns of scores and tie breaks, with abbreviated headings. "WIN" is fairly obviously the number of games won; "MMS" is the McMahon Score, the main ordering for the list; "SOS" is sum of opponents' MMS; "SODOS" is sum of defeated opponents' MMS; "CUSP" and "CUSS" are cumulative sum of points and scores (add the number of wins/MMS after each round); "WINS" can be printed as well as "WIN" if this is used for a tie-break.
There are two draw programs in common use in Europe. One is that produced by Germany's Christoph Gerlach called "MacMahon" and the other is "Godraw" produced by our own Geoff Kaniuk (windows version 6 was issued in 2005). The latter is the program used in the UK and has been successfully used at the European Go Congress. The big advantage for an organiser of using a computer is that they do not have to spend lots of time writing symbols and numbers on draw cards. Any recent problems encountered in using computers have usually happened because of organisers being unfamiliar with the system.
This page is one of a series which is indexed here.
The material on this page was written by Tony Atkins, and has appeared in the British Go Journal. Tony, and the Editor of the Journal, have kindly allowed it to appear here.