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Chess SA Rating system - Explanation (Third Article and last)

Chess SA Rating system - Explanation (Third Article and last)

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Malan77
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Chess SA Rating system can be a very complicated system and difficult to break down. In this Blog 3 will go into a little more depth.

First Article: Getting started on your Chess SA profile

Second Blog: Little more depth

Third Blog: Tying up the loose ends

We stopped after finding the Weighted Rating, but there were still a couple of loose ends:

  • Where do you get the Swe in the tournament
  • How to calculate the K factor for a tournament

HOW TO CALCULATE A RATED PLAYER’S RATING CHANGE FOR AN EVENT

  • Calculate his expected result (We) for each game played and subtract this from his actual
    result (S) to obtain Swe (Swe = S - We). 
  • His total rating change (ΔR) is calculated by summing the Swe (TSwe) scores and multiplying the answer with the tournament K-factor (ΔR = TSwe x K).

HOW TO CALCULATE EXPECTED SCORES (WE)

The following formula is used:
𝑊𝑒(𝑤ℎ𝑖𝑡𝑒)=0.541767+(0.001164×𝐷𝑤)
where
We = White’s expected score (Black’s expected score is simply 1- We)
Dw = White’s rating difference (white’s rating minus black’s rating) 

DIFFERENCE IN RATING

For updating of ratings only. For performances, the actual opponent ratings are used.

  • The rating difference (D) is the difference between the player’s own rating and that of his
    opponent. Thus, D = Rating (player) - Rating (opponent)
  • For the higher rated player, D may not be more than 390 (if it is, set it to 390). Thus, treat the opponent as if he was rated only 390 rating points less than the player himself.
    20.3 For the lower rated player, D may not be less than -460 (if it is, set it to -460).

K-FACTOR
K-factor is a number which determines the degree (by how much) a player’s rating will change.
The higher the K-factor, the greater the rating change (and vice versa).

The formula for K is the following:

𝐾=0.17113032𝑡+3.4643472

K = K-factor (rounded to 2 decimal places).
K may never be more than 24. If so then it’s set equal to 24.
K may never be less than 4.32. If so then it’s set equal to 4.32.
t = Time control (in minutes).