[mft_]

> It's not that good for top-level chess because a Magnus or Hikaru or basically anyone in the top few hundred players can bang out a series of extremely accurate moves in a critical spot - that's why they're top chess players, they're extremely good.

Interesting; I thought I'd read that even the very best players only average ~90% accuracy, whereas the best engines average 99.something%?

[tomku]

Top-level players regularly are in the 90-95% range aggregated over many games, with spikes up to 98-99%. If you have 98 or 99% accuracy over the course of an entire game (which happens sometimes!), it's either very short or you had significant sequences where you were 100% accurate. If that happened in one of my games it'd be clear evidence I was cheating, if it happens in a Magnus game it's him correctly calculating a complex line and executing it, which he does pretty often.

Edit: Even lower-level cheated games are rarely 100% accurate for the whole game, cheaters usually mix in some bad or natural moves knowing that the engine will let them win anyways. That's why analysis is usually on critical sections, if someone normally plays with a 900 rating but spikes to 100% accuracy every time there's a critical move where other options lose, that's a strong suggestion they're cheating. One of the skills of a strong GM is sniffing out situations like that and being able to calculate a line of 'only moves' under pressure, so it's not nearly as surprising when they pull it off.

[kmike84]

> whereas the best engines average 99.something%?

To compute accuracy, you compare the moves which are made during the game with the best moves suggested by the engine. So, the engine will evaluate itself 100%, given its settings are the same during game and during evaluation.

You get 99.9something% when you evaluate one strong engine by using another strong engine (they're mostly aligned, but may disagree in small details), or when the engine configuration during the evaluation is different from the configuration used in a game (e.g. engine is given more time to think).

[neaden]

Accuracy is a poor measure for cheating since better chess players will put you in a more complicated position. I'm not especially good but I've played some games with high accuracy just because I just did some book moves and the opponent makes a mistake. Accuracy was high but the correct moves were never especially hard to see.

[janalsncm]

Well accuracy is measured against the chess engine’s moves so it would be 100% by definition.