Accuracy example

On chess.com, I have analyzed several games by humans and even by machines. The highest accuracy I've ever seen is 99.7. I'm no expert at what contributes to a good or bad score, but I know the obvious; good moves equals higher accuracy store.

I have simulated a game with the highest-level CPU against itself. Even after analyzing it, the scores were only 99.7. Is 100 even possible? How do you determine the accuracy of 100?

  • 1
    When W offers a draw on move 1 and B accepts, that is 100 per cent accuracy.
    – Aravind
    May 23 at 10:01
  • 2
    please specify you're talking about accuracy on chess.com because there is no universal definition.
    – sleepy
    May 23 at 10:20
  • 1
    @sleepy unfortunately more and more people everyday think chess and chess.com are synonnimous
    – David
    May 23 at 20:18

Yes, 100% is possible. But having it happen doesn't mean much.

[FEN ""]

1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 6. Re1 b5 7. Bb3 d6 8. c3 O-O 9. h3

If you run this game through the analysis it will show 100% accuracy for both sides. All the moves are "book moves" which the analysis will give full credit for.

Now take the following game:

[FEN ""]
1. b4 1... g5 2. Bb2 f6 3. e4 h5 4. Be2 b6 5. Bxh5+ Rxh5 6. Qxh5#

It gives White an accuracy of 99.7, despite five "Best Moves" and one "Book". If I go to the Details tab, it gives White an accuracy of 99.68 on moves involving the queen (and also on moves involving the bishop or pawn.) But the only queen move was checkmate! So, for some reason, it's refusing to give 100% even on moves which are obviously best.

Don't make the mistake of taking those accuracy scores too seriously. The analysis runs only to a moderate depth and the results would change if it ran deeper (in your scenario with high-level engines playing against each other, the analysis would possibly mark some of the moves as not best just because it didn't see far enough to know why those engines played them.) And, clearly, there is something else going on which causes the analysis to not score moves as 100% even if those moves are perfect.

  • You could even play 1.e4, resign, and get 100% accuracy, right?
    – David
    May 23 at 20:17
  • Not all book moves get 100% accuracy. See chess.stackexchange.com/questions/31591/…
    – Zuriel
    May 24 at 1:52
  • 1
    @Zuriel Take the last move of the game in that link - the one NOT in book - out of the game, and run the report. 100%.
    – D M
    May 24 at 9:10

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