White vs Black advantage?

Currently, I use rybka to analyze my games, and I was wondering how I find my advantage, or disadvantage over my opponent. I'm wondering what it's called and what the different numbers mean. When analyzing a game, it says a move is + or - a number, what does it mean, is this to the overall advantage of one side? Any help is appreciated.

+= white is better    =+ black is better    +- white is winning             -+ black is winning          = position is roughly equal

 0.00 through 0.30 is basically even   0.30 through 0.70 or so is  white is better +=

  0.70  and higher is +- white is winning

  0.00 through negative -0.30 is even     neg - 0.30 through -0.70 is =+ black is better               neg -o.70 and up is winning for black

anytime either player reaches  1.00 or better or more  they are usually up material or have a forced series of moves leading to a win

computers factor in positional and material factors into this number

In the early opening the numbers are not always acurate if you are not in the computers book

If you have Aquarium you can see the %'s associated with the score.  Go to the Annotation section and click the evaluation tab.  You'll see a slider there with scores along with the corresponding win percentage.  According to the Rybka developers these are rough guidelines.  Internally, Rybka works with percentages and then converts them to centipawns for display.

.04 = 51%

.07 = 52%

.11 = 53% etc and so on

Here are the pecentages for various scores:

.33 = 59%

.64 = 67%

.98 = 75%

2.13 = 88%

5.50 = 95%