Computer Analysis - Blunders, Mistakes !? ?! etc.

What is the difference between a blunder, mistake, and innacuracy (not that I have ever made any...ahem).

Also, what are the meanings of and do these correspond to the following (I heard the following are not standardized and can mean different things to different entitites): ??, ?, !?, ?!, !!

!!: brilliant move

!: strong move

!?: interesting move

?!: questionable move

?: mistake

??: heavy blunder

Assuming the position is roughly even (no big advantage for either white or black), it works like this:

"Inaccuracy" - The computer evaluates that this move resulted in a position that is at least 0.3 points worse than the position resulting from the best move available

"Mistake" - This move is at least 0.9 points worse than the best move available

"Blunder" - This move is at least 2 points worse than the best move available - pretty bad!  :)

>> "Blunder" - This move is at least 2 points worse than the best move available - pretty bad!  :)

Interesting. This means that you could commit a blunder (??), yet still improve your point score by commiting the blunder. For example, let's say you are at +1.0 before you move. You might neglect a move that would have taken you to a +8.0 (best move available) and instead make a move to take you to a +6.0. This would be considered a blunder? Weird.

Aside from the obvious blunders that you know are bad moves, many moves assigned these categories are purely bogus. I recall one game that I won a piece down where the computer kept telling me I should shunt my King off to the side to keep it safe and be only "slightly worse" instead of using my King to usher in the pawns. So I'm not sure what it means by any judgment.

http://www.chess.com/echess/game?id=47068892

Actually, you won't be at +1 before you move, you would be around +8 due to your opponents blunder. When you then make your blunder, you might end up at 6 as you say.

Adding to your point about committing a blunder even though that blunder still leaves you in a winning position. I guess that the computer views it as a blunder because ultimately chess is about logic and making the most rational move possible and not winning in a round about way. However it can be deemed a mistake if you miss a mate in 2 say but get it in 3 or 4, for me that is dubious because it's still ultimatley a forced win.