In my recent game against IMVoja the Analysis says 7.O-O is a mistake and after 7...cxd4 (which is considered best) it says that 8.cxd4 is a book move. How does that even make any sense? A mistake followed by best play can't lead back into a book line. The opening explorer even gives 122 games with 7.O-O.
Computer analysis of limited depth is not given much weight in the opening.
7.O-O is a mistake and best play transposes into Milner-Barry Gambit, how does that make any sense at all?
7.O-O is a mistake and best play transposes into Milner-Barry Gambit, how does that make any sense at all?
Given evaluations like Mistake are based on the magnitude of evaluation change. As @notmtwain alludes to, take the evaluation out of the opening with a grain of salt, especially with lower depth analysis. A deeper analysis evaluates O-O as essentially 0.0 or close to it.
The computer analyses determine how much, in terms of Pawns, a particular position favors either side. the program is set to declare mistakes, blunders, etc. when the value of the position changes by a certain amount. That doesn't really mean it's a mistake, blunder, etc. - the best alternative move may not have been evaluated as being much better. But the programmer decided that -0.42 means "mistake" here regardless of where the best alternative is evaluated at -0.32 or +0.5.
Since the evaluation early in the game isn't very accurate, don't take it too seriously.
I should point out that anything leading to a book position CAN be a mistake if the alternative is much stronger. For example, you can set up positions where one side has a mate in one from a certain position but if he makes bad moves he ends up in a book position.
In my recent game against IMVoja the Analysis says 7.O-O is a mistake and after 7...cxd4 (which is considered best) it says that 8.cxd4 is a book move. How does that even make any sense? A mistake followed by best play can't lead back into a book line. The opening explorer even gives 122 games with 7.O-O so how can it be a mistake?