Expert Player level

What "Expert" means here

Every member of the club carries a Level of Play, and the level is not a mood or a slider. It is a measured playing strength, expressed in the number the backgammon world uses for exactly that: PR, the Performance Rating. PR is simple to state. Take every decision a player makes in a match, ask the engine how much each one cost compared with the best play, add it up, divide by the number of decisions, multiply by 500. Lower is better; zero is perfect.

An Expert's play sits in the band PR 4.0 to 6.0 — around one hundredth of a point per decision. This is tournament strength: the level of players who are seeded at international events and expected to reach the money. For orientation, a world-class human plays somewhere around PR 3 to 5 across a tournament; the upper half of the Expert band overlaps with that.

Why a target, and why not every Expert member plays the same

Each of the hundred Expert members has a target PR of its own inside that band. The target is what that member is tuned to average over many matches — not a promise about the next one. Two things follow.

First, no two Expert members are the same player. One sits near 4, another near 6; one is a little sharper on the checkers, another a little looser with the cube. Each was given its own fixed sharpness within the level, so that meeting GG Vassallo is not the same as meeting GG Yildiz.

Second, a single match will swing above and below the target, for a member exactly as it does for you. A match full of easy decisions produces a clean PR; a match full of close ones punishes everybody. The level holds as an average, and nothing is done to force one match into the band — no correction, no "making up for it" after a good game, no error budget being spent. That was tried in an earlier build and taken out, because people do not blunder on a schedule and neither should they.

How far from the top

The club's strongest player, GG Guru, plays the engine's best move every time: PR 0. An Expert member gives away around one hundredth of a point on every decision that Guru does not. Over a match that gap tells — but it does not decide everything, because the dice still exist.

Put in rating terms: an Expert member starts at 1900, Guru at 2300. On the club's rating scale, that difference gives the Expert member an expected chance of winning of about 39 % in a single game, 31 % in a 3-point match, 26 % in a 5-point match and 23 % in a 7-point match. The longer the match, the less the dice can do for the weaker player. Those are the odds against the very top of the club; against members of the levels below, they turn around.

How an Expert member is tuned

The engine underneath every member is the same one: GNU Backgammon, which reads every position at full strength. An Expert member does not get a weaker engine. What changes is how the member looks at what the engine sees: through a little noise, so that when two plays are close, the wrong one can look right. How much noise, and how often the member is sharp rather than careless, is set for the level and then adjusted per member.

The settings were not guessed. They were fitted to how real people at this strength actually err — around 200,000 decisions by approximately 100 real players, from world class down to PR 15.9 — and then confirmed in engine-graded test matches before the level shipped, played by hand after that, and re-measured every time the cast changes — by the time the doors open, every level will have thousands of graded games behind it. When an Expert member plays like one, that is because the measurement said so, not because somebody thought it looked about right.

Where they go wrong — and where they don't

An Expert's mistakes are the ones the engine finds and the player argues with: a marginally wrong play in a complex position, a slightly early cube. Everything clear is clean. The ceiling on a single decision is low, and what is left is judgement in positions that are genuinely difficult.

The cube at Expert level

Checker play and cube handling are tuned separately, because in people they come apart. An Expert's cube is sound: doubles on time, takes what should be taken, passes what should be passed, and loses only in the positions where the right answer depends on the match score to the second decimal. Their cube decisions are fitted to how players of this strength really handle it. Beating an Expert means playing at their level and rolling at least as well.

Is this your level?

If you have tournament results, know your own PR, and it sits in the single digits, this is where you belong. Play here and expect to lose matches you played well — and to learn exactly why from the review.

Your own level is not a label you pick. When you start, the badge beside your name says provisional. As your career goes on it fills in with your average Level of Play, measured the same way the members are: play in the Expert range and you carry an Expert badge; play better, and it moves. Try one level below yours for pleasure, and one above it to learn.

Beat them, and they are yours

In Career Mode, beat a member in a tournament or a league and they are unlocked for good — on your account, across every career you ever start. From then on you can sit down with them for a friendly whenever you like, or just say hello. The hundred members below are the ones that decide tournaments.