Dubov system

The Dubov system is a FIDE-approved pairing algorithm for Swiss tournaments. Like other Swiss systems, it works with scores, prevents two players from meeting more than once, and applies rules for colors and for players who must cross between scoregroups.

Its distinctive measure is ARO, short for Average Rating of Opponents. A rating is a numerical estimate of a player's competitive strength. After each round, the system calculates each participant's ARO from the ratings of the opponents they actually played.

Within a group of players on the same score, Dubov tries to bring their ARO values closer together. One of its ideas is to pair players who have so far had a low ARO with highly rated opponents. This aims to reduce differences in the average strength of opposition received by equally scoring players, although FIDE notes that a Swiss system can achieve that goal only approximately.

When a scoregroup cannot be paired by itself, the system can bring in players from lower scoregroups as upfloaters, meaning players moved upward to face someone with more points. This mechanism, together with the emphasis on ARO, distinguishes Dubov from the FIDE Dutch system.