Life In 19x19

thanks for the clarification but could you explain how you calculated exactly?
even though its not necessary it would be nice to be able to do it.

I am currently reading the endgame book of the "Elementary Go Series"

I added a sample of the pages
(ch 2 p.4f)

I dont understand the number "2 (-)" in the result.
And what do the plus and minus mean ??


Pls enlighten me