
BGonline.org Forums
Linearity
Posted By: eXtreme Gammon
Date: Friday, 14 May 2010, at 1:04 a.m.
In Response To: Linearity (eXtreme Gammon)
Note about the Elo system
The formula displayed on XG is the one use by all bg site. It is the same used in chess (Elo on wikipedia):
Basically the formula is Probability to win = 1/(1+10^(delo/factor))
 in chess the factor is 400
 in BG it is 2000/sqrt(N) where N is the match length^{1}.
So to get the probability of winning than in chess you can play 25 point matches. This is the number people have came up with using PR, which is an indirect way to reach it and tend to proove that the formula I gave for equivalence between PR and Elo (1 PR = 33 Elo) are about right.
^{1} I am not sure who came up with that formula, I think someone from FIBS. Checking about 200,000 games on Gammonsite gave very satisfactory results and tend to validate that hypothesis.

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