How the rating works
You win step size times surprise: the step comes from match length, the surprise from the rating difference — both numbers show before the match.
What the number means
Each of the five games has a number of its own, and every one of them starts at 1500. It is not a grade. It says exactly one thing: how a match between two numbers is likely to end. Somebody a hundred points above you wins a match to five points about fifty-six times out of a hundred — the number claims no more than that, and no less.
The scale is the one of the First Internet Backgammon Server, where the backgammon world has been putting itself into numbers since 1992 — the FIBS scale for short. So the marks experienced players carry in their heads mean the same here as there: a point here is a point there.
What a match moves
Two quantities decide how much a match counts: how long it is and how far apart the two numbers are. Pick the case that applies to you — the table works it out.
A gap of ±0 points, a match to 5 points: a win brings +2.9, a loss costs −2.9. Your chance of winning beforehand: 50 %.
- The longer the match, the more it moves. Over a single point the dice decide too often, and the number knows it.
- Beating the stronger number brings more, and losing to it costs less. That is the surprise from the rule at the top — and the reason nobody protects their number by avoiding strong opponents.
Computed for two settled numbers and a board with a doubling cube. A fresh number moves up to five times as far — that is not a bonus but ignorance, and it wears off quickly. In the games without a cube a match weighs a little less.
The rule, spelled out
Everything on this page fits into one line. It is the Elo rule chess has been computing since the sixties, with the adjustments backgammon needs: your number changes by the surprise, times a step size.
Δ = K · (s − p)
- K the step size
- How heavily this match weighs. It carries the match length, your own experience and a damper for opponents whose number is still wobbling. The scale is 1310 points wide; it decides how far a gap shifts the expected chance of winning.
- s the result
- One for the winner, zero for the loser. There is no third value — how large the win was does not count towards the number.
- p the expectation
- The chance of winning that the two numbers compute before the match. Winning against a small expectation pays a lot; winning as expected pays little. That is why the number cannot be farmed by picking weak opponents.
The bracket behind the number
Your number stands from the first rated match on, with its bracket: 1522 ± 228 means the number still knows little about you. The bracket only ever narrows — a pause leaves no trace on it.
The bracket is not decoration but the number's statement about itself: it says how sure it is. A fresh number does not know you and takes large steps; a settled one knows you and takes small ones. No bracket ever narrows past the noise floor of the computation, however long somebody plays — there are too many dice in this game for that.
Your number sways by about 34 points even when you play equally well. That is the dice, not you.
The six ranks
Above the number sit six dice ranks, hep yek to duses — fixed marks on the scale, never re-tuned. The badge is decoration: no rank ever unlocks anything.
The ranks are named after the six doubles — in the words that have been called out over Turkish and Persian boards for centuries: hep yek is double one, düşeş is double six. They are proper names; they are never translated, only transliterated. That way two players can talk about a rank without sharing a language.
- 1–1 hep yek < 1300
- 2–2 du bara ≥ 1300
- 3–3 duse ≥ 1450
- 4–4 dortcihar ≥ 1600
- 5–5 dubes ≥ 1750
- 6–6 duses ≥ 1900
Ladder points: the position inside the rank's band, 0 to 99.
What the board decided
What counts is what the board decided. A resigned or forfeited match moves the winner only by the points that were really on the table — the one who left answers for the full length.
Where new points come from
A match can destroy points. Create them it can only from your calibration account — it holds 300 points and never refills. That bounds, once and for all, how many points a career can carry into the leaderboard out of nothing.
The preview is the booking
The preview is the booking: both numbers freeze when the match begins, and what is booked after the last roll is exactly what stood on the screen before.