Before this crazy thing starts for good, and since I’ve never participated in any kind of tournament before, I thought it was a good idea to understand the rules. I thought there were in the Tournaments FAQ a simple answer to my basic questions : what the hell is a simultaneous McMahon and how does it work? But did not find … could someone provide a pointer to any “McMahon for Dummies” page? Thanks!
[edited : before anyone points to it, I tried to make sense of https://en.wikipedia.org/wiki/McMahon_system_tournament and https://senseis.xmp.net/?McMahonPairing but it seems there is some background reading I don’t have to understand those]
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Or be like me and don’t try and understand the ins and outs of all of tournament stuff. Leave all that to the TD. Just try and play your best in each game.
Sorry I can’t actually answer your question.
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You mean you don’t need to understand the rules at all to participate?
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Basically you’ll get 9 games (hence the name simultaneous), and the more you win the likelier it is you play stronger opponents the next round (it’s 12 rounds long), until the tournament finishes (this one won’t though). The McMahon part means that players with a higher rank start the tournament with more points than players with lower rank, decided by the McMahon bars. It makes stronger players more likely to play stronger players, and weaker players more likely to play weaker players.
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Well you need to understand the time limits of the games and probably how many games you’ll get at once (5-9) but other than that I don’t know what else is really necessary to know.
I think one can safely assume there are no time limits in this tournament.
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Stones of two colors, place on intersections, don’t get surrounded.
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… and stay safe and fit for a few more centuries. 
OK, thanks folks, that’s crystal clear.
One thing I was not sure was if all players were supposed to play all the rounds, but I understand behind your sarcastic lines that is the case, there is no elimination between rounds, so only the Final Time Out kicks you off once for all.
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The first timeout kicks you off. It’s a global rule. Don’t timeout a single game (of this tournament) or you’ll be kicked off (from this tournament).
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We’re already rubbing off on you! 
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As the designer of the original system, I will take the bait and try to do a simple version.
TL;DR
Your initial entry rank is a way of seeding you against other players of the same rank in the first round
After that, the better you do, the higher you’ll go in the rankings and the harder groups you’ll have in later rounds.
Conversely, the worse you do, the lower you’ll go and the easier your next round group will be.
You gain a point for every win. Final ranking will be based on your accumulated points.
End TL;DR
If you have hundreds, or thousands of players, in the same tournament, it is not a lot of fun for most players to play hugely mismatched games (like 5 dan vs 12 kyu or something). As a result, in real life a McMahon system sets a “bar”, which is a rank normally designed to have <= 8 players (for a typical 3 round tournament) on or above out of the tournament entrants. They start at (rank) points (so if the bar is 1 dan, everyone entering 1 dan or above starts with 1 point, 1 kyu start on 0 points, 2 kyus start on -1 points and so on down to the bottom of the rank entry list).
Pairing is then done on points, so effectively the top 8 play a single player elimination over three rounds, and everyone else gets paired up against someone of basically their own strength. You get a point for a win, and then you have a second round drawn the same way, but with first round winners one point higher on the table. So in this example the winner would have 4 points (started at 1, won three games), and a 3 kyu would have no chance of overtaking any of the top 8 (started at -3, after three wins has 0, and the top 8 all started at 1).
The problem with doing this in an online correspondence format (this event notwithstanding!) is that, with every round starting after every game in the last round finished, having a large number of games and results takes a very long time. So the idea when I created it was a similar system but with the top 14 players starting “above the bar” in two seven player groups where everyone has the same points, and with everyone outside of the top 14 starting with -1 points per rank (so if the bar was 1 dan with all top 14 players on or above this rank, someone entering at 10 kyu would start at -10, and be grouped with other -10s. However, as each player in this group plays 6 games against each other, each would have a score at the end of the first round of between -4 and -10, used to pair the groups for round 2).
With a tournament this size, playing 9 players at once in the same group means you have a chance of picking up 9 points in a round. Someone losing all 9 of their games starting at 1 kyu could easily be in the same group in the second round as someone winning all 9 of their games starting at 10 kyu, as they will start the second round on the same number of points. This process of updating points and re-drawing groups continues until the last round is complete, when everyone is ranked on their final score.
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@topazg Thanks a lot for taking the bait. At first reading my old brain did get only a vague idea. I guess I had to print it, translate in my native language, because as you might be aware of, you can get as fluent as possible in a non-native language, even think and dream in it, but forever you compute in your native language. So I’ll take a piece of paper, and draw stuff with French comments, and maybe I’ll grasp it at the end.
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As said above, not a native speaker, not sure I get the exact meaning of “rubbing off on” in this context.
A rubs off on B
A makes B more like A (usually through association of some sort)
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I have no idea what rank you are, but assume your first group will be amongst people of exclusively the same rank. You will play a round robin against all 9 other players, and your score will be your rank before you start playing (e.g. -6 if 6 kyu). You get a point per win, so if you win 5 and lose 4 games, your score at the end of round one will be -1 (-6 + 5).
Second round you’ll be grouped in with a bunch of people on -1 points (from 1 kyus who lost all their games, to 10 kyus who won all 9 of theirs). Again, round robin with 9 games, one point per win.
This repeats until all 12 rounds are completed - no eliminations (other than disqualification by timeout or people withdrawing by choice). Every round you get a point per win, and that total keeps going until the end of the tournament, at which point everyone is ranked in order of their final score 
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Not one either. 
Too many movies, I guess. 
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I have no idea either 
The one given by my profile is currently 16 kyu, whatever that means. (I will certainly understand McMahon before having understood how the rank is computed).
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