Setting McMahon bars

I am trying to set up a series of regular tournaments for high DDK in the (perhaps hopeless) attempt to get better by playing more balanced games, but I am a bit stumped by the McMahon bars’ settings.

I have read the other posts on the subject as well as the page, but there seems to be some kind of magic and a a strong subjective element in how the bars are set. In my case, I am setting up a 3-round tournament for 25k-15k players, and (from previous experience), I expect between 5 and 8 players to participate. Sensei’s “bar theory” (love the term) says that:

  1. players above higher bar should all have an equal “probability of winning”
  2. players below lower bar…have all equal probability of not winning?

Then various options are presented on how to set (1) and (2), which depends on desired outcome (single winner with no tie breaks, reliable ranking, etc.), number of participants, etc. It all makes sense for a big tournament but it seems way overboard and mostly inapplicable to a small one. And furthermore, some of the rules require that I wait until registration is closed to set the bars, whereas the OGS form asks me to specifies them when the tournament is created.

Can anyone provide some basic advice?

FWIW, I could never get to the bottom of what OGS McMahon setup does.

IE it’s not just you :slight_smile:

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OGS uses the single band method for calculating the initial MM-scores. But I think OGSs McMahon will not suit your need for more balanced games. As far as I know the pairing methods don’t account for McMahon score of each player. If you want balanced match making set the pairing methods to strength. That will match players with close ranks against each other.

On OGS the tournament director can change the points of each player after the tournament started and before it ends, so you could customize the points as you wish after the tournament started.

Single rank bands

This is by far the most common system. For every additional kyu and/or dan rank, a player recieves an extra point. If a 10 kyu has 0 points, then a 5 kyu gets 5 and a 1 dan gets 10. This system usually contains two bars, the top bar and the bottom bar. The top bar defines the strength above which all players are in the same band. This band contains the strongest players, who are said to be above the bar, and should contain all players that are thought to have a chance to win the tournament (for more details see BarTheory). The bottom bar functions the same way, but defines a playing strength below which all players are in the same bar, usually to avoid large gaps in the starting bands.

For that few players I don’t see how McMahon should work in any case. For McMahon to work you need many players within the same McMahon-band. With OGSs single rank bands you would even fix the winner in advance since 1 point per rank difference equals 1 point McMahon initial score.


Everyone who has a chance to compete for the first place should be above the upper bar, everyone who has a chance to ‘compete’ for the last place below the lower bar.

For example having the upper bar at 10k and the lower at 20k might make sense in your case.

However: If you only have 5-8 players, they might not be distributed evenly across the ranks. Why go for a McMahon at all? Round Robin should do nicely.

And finally: McMahon is broken on OGS anyway, so avoid it. (Simultaneous McMahon is fine though.)

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If you want to play balanced games, don’t play tournaments. Better use quick match finder or custom game with tight rank restrictions. In my experience tournaments don’t result in balanced games.