When in chess notation do moves get double exclamation points(1.e4!!) instead of a single one?(1.e4!) 

Usual a double exclamation is used when a move is truly phenomenal... (Qxg7+!! (mate in 8) ...

 

Big sacrifices, etc...

 

A single exclamation is better used when someone tactically exploits someone elses blunder.

 

 This may not be 'accurate'.. you basically get a 'feel' for it.

http://en.wikipedia.org/wiki/Algebraic_chess_notation

http://www.markalowery.net/Chess/Notation/notation.html 

"!" means that the move is good. "!!" indicates a brilliant move, like if somone plays a move that is especially astonishing.

Thanks for the info.

I usually give !! s based on several criteria:

1. Depth of the move

2. Originality of the move

3. Creativity of the move

4. Difficulty of the move to find