The ELO system, developed by physicist Arpad Elo for chess in the 1960s, calculates expected match outcomes and updates ratings based on actual results. The formula: expected score = 1 ÷ (1 + 10^((opponent_rating − own_rating)÷400)). The K-factor determines how much ratings move per match — higher K means faster movement. ELO has been adapted for table tennis (ITTF uses TTR, a variant), football, American football and many other sports. In table tennis, beating a higher-rated opponent gains more points; losing to a lower-rated opponent costs more.
Key points
- Developed by Arpad Elo for chess, 1960s
- Expected score = 1/(1+10^((Rb-Ra)/400))
- K-factor controls how fast ratings change
- Adapted for ITTF table tennis (TTR system)
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