Match Navigation #

June 7, 2021 8:31 am

This section of the site shows you how to navigate matches and games. Above this text is the match title and subtitle. The title usually contains the contenders (e.g. Bottom Player vs. Top Player) while the subtitle usually contains the starting date and time of the match. Occasionally, the subtitle also contains the category of the match.

Below the subtitle are buttons to download match files and to start watching the match. You can use either GNU Backgammon (GNUBG), eXtremeGammon (XG), or your favorite backgammon program to open the MAT file; but at the time of writing, GNUBG cannot open XG files. Both of these files contain the complete move list of the match, but the XG file contains the analysis and rollout information used.

Now we move on with the tables below. Headings are used to emphasize them, but the headings in actual match pages will contain more vital information.

Equity Lost #

To understand the tables, one must first have a basic understanding of equity lost. Most modern backgammon programs use equity loss to determine how well a player played; in this case, XG uses the normalized equity the player lost per decision.

Equity #

Warning: What I discuss here is a massive oversimplification of what people call equity. If you find more detailed information that disagrees with what I say, it is more likely that I am incorrect or have intentionally omitted a case.

Equity deserves a page of its own, and is briefly discussed on the GNUBG manual. For our purposes, we can say that equity describes how likely we are to win the game. A positive value means that the player is winning, and a negative value means that the player is losing.

The “normalized” in “normalized equity” means that the equity is adjusted from the match score to a common point of view. GNUBG normalizes the equity to a money game (unlimited match).

As a rule of thumb, \(+1\) would mean the player is set to win 1 point (a single game), \(-1\) would mean the opponent is set to win 1 point, and the same is true for \(\pm 2\) (a gammon) and \(\pm 3\) (a backgammon).

Decision #

A decision is a checker move or double action that isn’t “obvious” to the computer. The XG manual defines the following as obvious:

• A forced move
• A move for which the best choice and the worst choice have an equity difference of less than 0.001.
• A double action where the equity before doubling and after doubling is the same (optional double)
• A double action where the equity before doubling is 0.200 larger than the equity after the double (obvious non double)
• A double action where the equity before doubling is 0.200 larger than the equity after a drop (obvious too good to double)
• A double action where the equity before and after a double is very negative (less than -0.900). This corresponds to a loss of position when trailing in the match by a lot

and the following as not obvious:

• A double decision resulting in a double
• A take decision

Equity Lost Per Decision #

The equity lost per decision that XG uses is a mean. The numerator is the sum of the equities lost by the player from making wrong decisions (compared to the best option) and the denominator is the number of decisions the player had to make.

As an example, let’s say a player, in 12 checker play decisions and 4 cube play decisions, made a checker play blunder worth -0.125 in equity and a cube action error worth -0.025 in equity. This is how to compute the equity lost for checker play, for cube play, and in total.

Qualitative Ratings #

Most modern backgammon programs also provide a qualitative rating for the mean equity lost. XG has its own system of rating with various intervals, and here I will only show the ranking. Do note that you should not take these ratings as gospel or at face value, and if you intend to use them to gauge how much you’ve learned, the most important part is the ranking shown here, with increasing error and decreasing “skill”.

1. World Champ.
2. World Class
3. Expert
4. Advanced
5. Intermediate
6. Casual Player
7. Beginner
8. Distracted

Performance Rating #

XG has its own system of describing overall performance called Performance Rating (PR), and it is equivalent to the negative of the mean equity lost times 500. One way to interpret this is that one PR point is equivalent to half of a thousandth of an equity point lost. Though it seems an error of -0.0001 is small, people talk in thousandths of an equity point (also called millipoints) because their game could be that one in a thousand games where they lose but could have won.

For our purposes, we can say that a lower PR is always better.

Match Overall Rating #

Bottom Player	Category	Top Player
Advanced (-0.0213)	Total Error	Distracted (-0.5024)
Casual Player (-0.0372)	Checker Play	World Class (-0.0085)
World Champ. (+0.0000)	Cube Play	Distracted (-1.0662)
10.64	Performance Rating	500.00

This table shows you how well each player did at a glance. Beside each qualitative rating is the mean equity lost for that category. You can see here whether a player committed more errors in their checker play or cube play, and if a player committed fewer errors than the other. It also shows the PR of a player for the match.

Game by Game Rating #

Bottom Player	Game by Game	Top Player
Intermediate (-0.0298)	Game 1	Distracted (-0.4333)
World Champ. (+0.0000)	Game 2	Distracted (-0.8481)

This table shows you how well a player did for each game. Similar to Match Overall Rating, beside each qualitative rating is the mean equity lost for the game. You can see here which games a player committed more errors in (a good way to find out which games to scan), and where a player committed fewer errors than their opponent. This table also has links to each of the games in the match.

Match Detailed Rating #

Bottom Player	Category	Top Player
1 (1) -0.1490 (-1.482%)	Move Errors Equity Lost (Cost)	1 -0.0341 (-0.348%)
0 +0.0000	Double Errors Equity Lost (Cost)	1 (1) -0.5648 (-5.618%)
0 +0.0000	Take Errors Equity Lost (Cost)	1 (1) -1.5677 (-39.311%)
1 (1) -0.1490 (-1.482%)	Total Error Equity Lost (Cost)	4 (3) -3.0147 (-65.974%)
1 -0.2173 (-11.996%)	Jokers Luck	1 +0.2173 (+11.996%)

This table shows you the collected details of the whole match; a more detailed version of Match Overall Rating if you will. It shows the move/double/take errors and if any, parenthesizes the number of blunders in those errors. It also shows the equity lost and the cost. The cost for matches is in terms of match winning chances (the likelihood of winning the match).

You can also find in this table the number of jokers each player rolled and the amount of equity contributed by luck.