Since its creation in 2008, Safe Harbor Games has become a microcosm of the online gaming community at large. It provides a community based gamming site that has attacted players from around the world and from many other gaming sites. For one group in particular, we have attracted competitive Backgammon players who not only compete in group tournaments, but also play against each other to hone their own playing skills by playing against other players who skills were equal or better than their own.

One of the first Backgammon servers to offer a way for players to rate each other was FIBS (First Internet Backgammon Server). All backgammon players on FIBS have a rating. The higher the rating, the better skilled the player is and since every player has a rating, you can easily determine whether a particular player was the one you want to play.

FIBS rating method, derived from the ELO rating system used in professional Chess, is the gold standard that many game sites, including Safe Harbor Games, has adopted for their own rating system.

The FIBS rating needs three pieces of information to determine a player's rating:

1. Current rating of both players
   If the player has no current rating, then their rating is set to 1500.
   The ratings for most players will fall between 1000 to 2000 with the higher the rating, the better the skill.
   The greater the difference in ratings, the more likely the higher rated player will win. Also, the longer the match length, the more likely the higher rated player will win.
2. Current experience
   Experience is the sum of all the match lengths that the player has either won or lost. A new player will start out with an exerience of 0.
   The lower the experience, the greater the effect on the ratings change.
   Players with experience of 400 or more are considered "experienced" players, and their experience no longer affects the rating change.
3. Match Length
   The match length is the length agreed upon at the beginning of the match and NOT the number of points won at the end.
   The greater the match length, the greater the effect on the ratings change.

Our routines determine the ratings and experiences for both players when the match is over. Please note the formulas shown below are to illustrate the complexity of the calculations. The actual programmed calculation flow may be different, but the results are the same.

• n = Match Length.
• P1 = Winner's Rating
• P2 = Loser's Rating
• E1 = Winner's Experience
• E2 = Loser's Experience
• D = Difference between the two Ratings
  abs(P1 - P2)
• U = Probability of the underdog (lower rating) winning the match
  1/(10^(D*sqrt(n)/2000))+1)
• F = Probability of the favorite (higher rating) winning the match
  1-U
• PE1 = Modifier based on Winner's experience
  PE1 = max(1, ((500-(E1 + n))/100))
• PE2 = Modifier based on Loser's experience
  PE2 = max(1, ((500-(E2 + n))/100))

• Winner's change in Ratings
  + (4*PE1*sqrt((double)n)*U)
• Loser's change in Ratings
  - (4*PE2*sqrt((double)n)*U)
• Change in Experience
  + n

There is a general belief that if you want to find a match with a player of roughly the same ability, look for someone with a similar rating, or if you want to play someone who is a better player, look for someone with a higher rating than your own. In any rated room, mouse over the player in the population list on the right side to see their rating.

This method will get you a rough idea of who to play - the greater the experience, the more accurate the ratings usually are.

Ratings are calculated and updated as soon as the match is complete.

Unfinished rated matches are resolved by the system after 48 hours. The player who leaves the table first, is determined to be the loser.
The one difference in calculations for unfinished matches, is the loser of the match receives twice the loss of points to their ratings. This is done to encourage players to finish their matches, even if they lose the match.

• The FIBS Rating System