General Info on the rating system
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The system used for rating is the "ELO System" which is being used by
DCI who took it over from the Chess Rating. New players start at a
rating of 1600. The rating scale is logarithmic, which means that the
difference in rating between two players always reflect the probability
that one player wins over the other. The scale is such that a rating
difference of 123 means that the probability of a win is in the
ratio 1:2.

Our ratings
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Within SWAD we consider 5 ratings:
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CoD:    Continuous Draft only
Lim:    Includes Continuous Draft and "sanctioned" limited events
ABC:    Constructed format using the ABC-common rules
Com:    Combined rating including all of the above
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CIC:    Champion Impersonation Challenge, try to be someone else :-)
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The two first are based on counting duels, the two next are based on
count of matches, the last is a bit special and will be ignored for now.
The scatter in the rating system is pretty large, a rough number for the
1 sigma on a single rating is around 25. Therefore, differences in
rating less than 40 are certainly not significant. Ratings for players
with less than 8 matches(duels) are meaningless, only above 12 do they
start to give a useful hint.

Added features
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Because of the log nature of the ratings, the only thing that matters is
the differences, i.e. one can shift the zero-point as one likes to.
Since SWAD has players leaving at regular intervals (taking points away
with them), I usually add a zeropoint to all ratings such that the
mean/median of "active player ratings" remains close to 1600.

Players that have left remain in the ratings, but after a while I start
to let their ratings drop. I.e. players that have not played a duel for
a full year will slowly drop in the ratings. This is fair as they cannot
be challenged. As soon as they play a match for rating points they will
get their old rating back.

Limited ratings
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Limited ratings are calculated on the basis of all CoD duels and all
other "Limited Format" duels (e.g. drafting) played under the initial
agreement/announcement that the event would count towards player rating
(sanctioned events). First sanctioned draft event was the CoD/Rochester
SWAD event on 12.06.05. Limited and CoD ratings are both calculated on
the basis of individual duels.

Posting schedule
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CoD/Limited/Abc/Combined ratings will be calculated and posted at
irregular intervals (as soon as enough new duels/matches have been
played to make a new posting relevant), but they will always be
"out of phase".