found this exact same question already asked on the forums at http://www.chess.com/forum/view/general/what-does-the--after-analysis-mean and this is an answer a tactics moderator posted "
you will find out more, by learning more about portable game notation.
PGN.
http://en.wikipedia.org/wiki/Portable_Game_Notation
NAGs are Numeric Annotation Glyphs - a code set up to facilitate computer use for evaluating positions.
http://en.wikipedia.org/wiki/Numeric_Annotation_Glyphs
A Numeric Annotation Glyph is composed of a dollar sign character ("$") immediately followed by one or more digit characters. Each NAG then has a specific meaning and often a standard typographical representation. The meanings first defined stemmed from the use of specific typographic symbols when annotators were commenting upon chess games; most especially in Chess Informant [2] publications. The objective was to devise an alternative representation of these symbols which could be incorporated in the simple computer file format proposed as the PGN standard. This mechanism allowed often sophisticated typography to be expressed using the simple ASCII character set.
Since its inception there has been no attempt to further formalize or standardize the meaning of the undefined 115 NAGs
$18: white has a decisive advantage + -
$19: Black has a decisive advantage - +
I hope this helps you understand better as you work with the analysis lines provided.
tactics moderator "
so its just a number that computers use as indicators for the evaluation, humans shouldn't worry about it.
It's found at the end of analysis on Tactics Trainer and maybe elsewhere. Highlighted below. Can't work out what it is. It's going to be something stupid I bet. Any clue?
({12:-6.20} 35. Rxf5 Qe1+ 36. Kh2 Rxh4+ 37. Qxh4 Qxh4+ 38. Kg1 Ka7 39. Rf2 Kb6 40. Rf3 Kc5 $19)
({12:+0.21} 35. Qg3+ Ka7 36. h5 Qh4+ 37. Qh3 Qxh3+ 38. gxh3 f4 39. h6 Rc6 40. Rxf4 Rxh6 41. h4 Kb6 42. Kg2 $10)
({12:-0.24} 35. Qxf5 Qxh4+ 36. Kg1 Qd4+ 37. Kh2 Qh8+ 38. Kg1 Qb2 39. Rf2 Qc1+ 40. Rf1 Qd2 41. Rf2 Rc1+ 42. Kh2 Qd6+ 43. g3 Kc7 $10)
({12:-1.49} 35. Qd8+ Ka7 36. Qd2 Qxh4+ 37. Kg1 Rc5 38. Qe3 b6 39. Qd3 Qe4 40. Qxe4 fxe4 41. Rf7+ Kb8 42. Re7 Rc4 $17)