Backgammon Game Analysis: How to Read Your PR
Analyse your online backgammon games in the Gammon42 app with GNU Backgammon. See your PR, blunders, luck and the best play for every roll.
After an online game, Gammon42 can go through every decision you made with GNU Backgammon, the open-source backgammon engine, and show you how well you played. You get one number for the whole game (your PR), a mark on every costly play, the dice luck of both players and, for each roll, the plays the engine preferred.
The analysis runs on our servers, not on your phone. It is in the Gammon42 app for iPhone and Android from version 1.4.0, and it works on finished online games against another player.
How to analyse a game
Right after the game
- Finish an online game: Ranked, Boosted, Friend or Tournament.
- On the result screen, tap “Analyse game”.
- The button changes to “Analysing your game…”. When the analysis is ready, the line above the buttons shows your PR, your blunders and your luck, for example “PR 8.4 · 2 blunders · Luck +0.310”.
- Tap “Review” to open the full analysis.
Later, from your game history
- In the main menu, tap your picture and name at the top to open your profile.
- On the “Profile” tab, tap “Game history”. Your finished online games are listed by day, newest first. You can filter them with “All”, “Won” and “Lost”.
- Find the game and tap “Analyse game” on it.
- While it runs, the game shows “Analysing…”. It usually takes under a minute, and you can leave the screen in the meantime.
- When it is ready, the game shows your PR and your rating. Tap the game to open the review.
If an analysis costs Sparks, the price is written on the button, and in Game history the app asks “Analyse this game?” before it starts.
How to read the result
The analysis screen is called “Game analysis”. It has two tabs, “Review” and “Summary”, and a switch for “Simple” or “Expert”. Simple keeps the figures short. Expert adds gammon and backgammon chances, cubeful equities and the cube table. The app remembers your choice.
Your PR
PR is the main number. It is the equity you lost per decision, multiplied by 500. Only real decisions count: checker plays where you had a choice, and close cube decisions. Forced moves are left out.
Lower is better. A PR of 0 means you lost no equity at all: every decision matched GNU Backgammon’s choice. For example, losing 0.300 equity over 30 decisions gives 0.300 ÷ 30 × 500 = PR 5.0.
The app colours your PR so you can read it at a glance:
| Your PR | Colour in the app |
|---|---|
| under 7.5 | green |
| 7.5 to 12.5 | blue |
| 12.5 to 15 | amber |
| 15 or more | orange |
Your PR is never shown in red. A high PR is not a defeat, it shows where you can improve.
The Summary tab also splits your PR into “Checker play” and “Cube play”, so you can see which part of your game cost more.
The rating name
Next to your PR, under “Performance rating”, you see a name from GNU Backgammon’s own rating scale. The engine picks it from the same figure as your PR: the equity you lost per decision. From best to worst:
| Rating | Step on the scale |
|---|---|
| Supernatural | 7 (best) |
| World class | 6 |
| Expert | 5 |
| Advanced | 4 |
| Intermediate | 3 |
| Casual player | 2 |
| Beginner | 1 |
| Awful | 0 |
The Summary tab also draws your PR on a bar from 0 to 25, with rating names along it.
Equity lost
Equity is GNU Backgammon’s estimate of what a position is worth, in points. For every move, the engine compares your play with its best play. The difference is the equity you lost on that move. Simple mode shows it with two decimals (−0.08), Expert mode with three (−0.083).
Doubtful plays, mistakes and blunders
Costly plays get a mark, the way analysis programs print them:
| Mark | Name in the app | Equity lost |
|---|---|---|
| ?! | Doubtful | 0.03 or more |
| ? | Mistake | 0.06 or more |
| ?? | Blunder | 0.12 or more |
These are GNU Backgammon’s default thresholds. A play without a mark is a “Best move”, or a “Good move” when it lost only a little.
Cube actions get their own verdicts: “Missed double”, “Wrong double”, “Wrong take” and “Wrong pass”, or “Correct double”, “Correct take” and “Correct pass”. In the Summary, cube errors are counted under Cube play, not with the checker-play marks. If the cube is new to you, start with what the doubling cube is.
The Review tab: move by move
The Review tab shows the real board, with the position before each decision and the dice that were rolled. It opens on your first marked mistake, or on your first move if you made none.
- The verdict. A title (Best move, Mistake, Blunder…) and one sentence that names the better play and what it does: hits the blot, makes a new point, keeps the checkers safer, and so on.
- “Alternatives”. The best plays for that roll, best first. In Simple mode each one shows how much it loses against the best. Tap a play to see it on the board: your move is drawn in dark ink, the other plays in green, and a red ghost checker marks a hit. Simple lists the top 3, Expert the top 5, and your own play is always included.
- “Winning chances”. Your share of the win after the move.
- Luck and pips. How lucky the roll was, from “Very unlucky” to “Very lucky”, and the “Pip count” (“You lead by…” or “You trail by…”). To count pips yourself at the board, see pip counting.
- “Moves”. The full move list with the dice, the moves, the marks and a luck mark (++, +, −, −−). Filter it with “All”, “Mistakes” or “Mine”.
“Next mistake” jumps to the next marked play. You can also swipe across the board to step through the game.
The Summary tab: the whole game
- A card for each player: PR, rating name, Checker play, Cube play, “Dice luck” and the number of doubtful plays, mistakes and blunders.
- Winning chances through the game: a chart of your winning chances, move by move. Dots mark blunders. Tap one to jump to that move.
- “Biggest mistakes”: the costliest marked plays of the game, up to five, from either player. Each row shows who played it and the best play. Tap a row to jump to that move.
- “Dice luck”: the luck of both players and one sentence on whether the dice or the quality of play decided the game.
Luck
GNU Backgammon gives every roll a luck value in equity: positive when the roll helped you, negative when it hurt. The app adds up the luck of all your rolls. On the player card, above +0.30 shows as “Lucky”, below −0.30 as “Unlucky”, and anything in between as “about even”.
If a power-up changed the dice during the game, the luck figures are hidden (“Luck hidden: power-ups were used”), because those dice did not come from a normal roll.
What it costs
- Free each month. Free players get a number of free analyses every calendar month (UTC), for their most recent games. The top of Game history shows how many you have left this month.
- Recent games. An older game, outside the recent-games window, shows “Older game”. Analysing it needs Pro.
- Used up. When you have used this month’s analyses, the app shows “Free analyses used up”. They come back next month.
- Failures don’t count. An analysis that fails, or a game that can’t be analysed, doesn’t use one of your free analyses. If an analysis fails, you can ask again.
- Sparks. An analysis can also have a price in Sparks. When it does, the price is on the “Analyse game” button. If the analysis fails or the game can’t be analysed, the Sparks are refunded.
- Pro. With Gammon42 Pro there is no monthly limit, you can analyse any game in your history, and an analysis never costs Sparks.
- One analysis per game. Both players share the same analysis. If your opponent has already analysed a game, you can open it from Game history without using one of your own.
You can only have a few analyses running at the same time. If you reach that limit, wait for them to finish and try again.
Which games can be analysed
Yes: finished online games against another player, in every mode: Ranked, Boosted, Friend (see playing with friends online) and Tournament. Tournament games are analysed as part of the match, with the score at the time; the Summary then shows, for example, “5-point match”. Cube decisions are analysed when the cube was in play.
No: games against the computer and games for two players on one device. They are played on your device, not on our servers, so they don’t appear in Game history.
Some online games show “Not analysable”, with the reason under it:
- “No moves were played”: the game ended before anyone moved a checker.
- “Game not finished”: no result was recorded.
- “This game couldn’t be replayed”: the recorded game could not be rebuilt move by move. The app would rather show nothing than give advice on the wrong position.
Now and then a single move shows “Not analysed”, for example a roll made with power-up dice that standard backgammon doesn’t have. The rest of the game is analysed as usual.
Tips for using the analysis to improve
- Start with “Biggest mistakes”. Look for the rows with your name. A few large errors usually cost more than many small ones, so fix those first.
- Guess before you look. On a marked move, decide what you would play now, then open the Alternatives and compare.
- Read the reason. “Hits the blot”, “makes a new point”, “keeps the checkers safer”: the same reasons come back game after game. Spotting them at the board is the real gain.
- Check the cube on its own. Compare your Checker play and Cube play figures. If most of your lost equity comes from the cube, work on doubling and taking before anything else.
- Watch the trend, not one game. Your PR moves a lot from game to game. Compare it over several games of the same kind.
- Separate luck from skill. After a loss, the Dice luck card tells you whether the dice or the play decided it. Both happen.
More questions about Gammon42? See the FAQ.
Frequently asked questions
What is PR in backgammon?
PR is the equity you lost per decision, multiplied by 500. Forced moves don’t count. Lower is better: a PR of 0 means every decision matched the engine’s choice. Gammon42 calculates it with GNU Backgammon after each online game you analyse.
Is the game analysis free?
Free players get a number of free analyses every month for their most recent games, and Game history shows how many are left. An analysis that fails doesn’t count. With Gammon42 Pro there is no monthly limit and you can analyse any game in your history.
Can I analyse games against the computer?
No. Only finished online games against another player can be analysed: Ranked, Boosted, Friend and Tournament games. Games against the computer and games for two players on one device are played on your device and don’t appear in Game history.
How long does an analysis take?
Usually under a minute. You don’t have to wait for it: the analysis keeps running on our servers, and the result appears in Game history when it is ready.
What is the difference between a mistake and a blunder?
Both are plays that lost equity against the engine’s best play. A doubtful play (?!) lost 0.03 or more, a mistake (?) 0.06 or more and a blunder (??) 0.12 or more. The app shows the exact amount next to each marked play.
Can my opponent see the analysis of our game?
Yes. There is one analysis per game and both players can open it. If your opponent has already analysed the game, you can open it from Game history without using one of your free analyses.
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