Thanks for all the great replies!  I look forward to sitting down with NCO and going through some of the +- lines of my openings to see if I can understand where the advantage lies.

Thanks!
Scott

One might use a negative definition: += means that Black can afford less suboptimal moves than White. I think it was Lasker, who said, that it needs two mistakes to get a lost position. If that is true, += means that one mistake will cost Black the game, while White still can afford one or even two.
Personally I also use it in the meaning "I would rather have White than Black, but with correct play the game will end in a draw."
What is the difference between ± and +- ? Never really grasped that one. Yes, we always read "White is much better" and "White has a won position". I have always felt, that much better positions should be won. Where am I wrong?

Well...when I was first trying to make sense of these evaluations, I came to a weird realization one day. I was playing through Silman & Donaldson's "Exchange Slav" book, and I came across the following position: 1. d4 d5 2. c4 c6 3. cxd5 cxd5 4. Nc3 Nf6 5. Nf3 e6 6. Bf4 Nbd7 7. e3 a6 8. Bd3 b5 9. h3 Bb7 10. 0-0 Be7 11. a4 b4 12. Ne2 0-0 13. a5 +/-. And normally I don't spend much time on weird side-lines, but I couldn't let this one go. I remember thinking, "Wow, white has a clear advantage and I have no idea what it is. And if I got this position in a game, I bet I would lose." And then I realized, who cares about += advantages when you can't even do something with +/- advantages. So starting with this position, I made it my job to learn to recognize +/- positions, and be capable of picking them apart, understanding them, and forming reasonable plans based on my assessment. A good way to do that is go through a book or NCO for whatever opening you play, and only look at the +/- positions, and try to come up with plain english explanations for why one side is better.

OstapBender wrote on 06/27/06 at 17:50:13:


Fischer,Capablanca,Karpov & to some extent Spassky are excellant examples of players being able to squeeze out wins from minute advantages or seemingly equal positions (to most people)

OstapBender wrote on 06/27/06 at 16:12:12:


I would argue with those numbers.  For instance, I would say that (in general) +1.0 is a clear advantage bordering on a decisive one, not a slight advantage bordering on a clear one.  (Reminds me of a quote from Pal Benko:  "A pawn up for nothing is a winning advantage.")

I recall Fritz using values about like these:  equal is less than a .3 pawn advantage for either side, slight advantage is anything from that up to .7 pawn, clear advantage is from there up to 1.2 pawns, winning/decisive advantage is greater than that.      

I agree very much with Keano.

A beginning chess player learns the moves and a few names of openings.

An intermediate chess player begins to learn the lines.

An advanced chess player starts to look for ways to play lines in his own style.

A player who wants to be truly competitive has opinions on variations based on experience and taste.  Those opinions are stated in terms of +=, =, =+.  There are very few positions that are truly equal that aren't just plain drawn.  One side or another has some sort of extremely small advantage.  

The goal and the test of a great player is to take the elements of the position that are advantageous to him and turn the position into a win.

For everyone below a certain level, the differences between the three symbols can't really be described as computers do, by the amount of tenths of pawns one has.  It may be more useful to ask yourself the following questions:

* Which side has the initiative, and is there any compensation for the side without the initiative?

* Which side would I rather play, and why?

*Which side has the advantage in an endgame, and is this a big enough advantage to worry about losing?

In assessing endgames, I often ask myself whether I would have better chances of winning/drawing with certain pieces/pawns on the board.  

After the game, I go back and try to make formal decisions about where White lost the advantage or Black gave up too much.  (I believe that while chess is theoretically drawn (=), White has a small advantage (+=) from the beginning. )  One of the best things a player can do when analysing his or her own games is to determine where the crucial turning points in the game were, and why.

Also, when annotating games for publication, I simply avoid those symbols and describe the advantages and chances for each side.  Reviewers have often stated that such symbols that you have pointed out plus the unclear signs are often just a way for an annotator to stop his lines of analysis (and is often called lazy for doing so).

I know I went a bit off topic, but I hope this answers your question to some extent.

There are different interpretations, but very roughly (someone feel free to correct me if this is a bit off although I don't think there is universal agreement anyway) the symbols translate to:

+= or =+  0.25-1.0 pawn advantage (i.e., equivalent value)

+/- or -/+ 1.0-2.0 pawn advantage.

+- or -+ >2.0 pawn advantage.

I've also seen the symbols correlated with winning percentage but don't recall details.

I never found += or =+ very useful in 'understanding' a position without an accompanying verbal explanation/assessment.