Hello, I don't understand the post-game summary(mistakes,blunders,missed wins). I would like to know how these are generated. The summary of one of my games is 0,0,0, but the analysis contains 1 missed win. Is it an engine report at a low depth? Also, sometimes when you reload the page, the numbers change. Why is that? Thank you.
The summary and specifically "accuracy" is called chess.com "CAPS" (Computer Aggregated Percentage Score). How computers calculate this is an interesting discussion that can be an article in itself and various chess engines calculate this slightly differently. The short version of what happens is basically the computer calculates a bunch and then assigns an evaluation at the end of the long line(s). The computer then chooses to play the move the results in the line with the evaluation most in their favor (as far as the computer can currently calculate).
It calls their choice the "best move" and then evaluates the other moves and lines as worse by however many "centipawns" it judges. A centipawn is a unit the computer uses to judge chess positions; one centipawn is worth 1/100 of a single pawn. Evaluations that are positive favor White and negative favors Black. An evaluation of (+0.29) is favoring White by 29 hundredths of one pawn. An evaluation of (-0.78) favors Black by 78 hundredths of one pawn and so on.
If your chosen move is a certain amount "worse" than the "best move" then it declares such move a "blunder." Similarly, "mistakes" are smaller blunders and "inaccuracies" are even smaller than mistakes.
The reason why the numbers (evaluation) sometimes changes even upon reloading the page is because the computer might calculate slightly longer one time versus another, so it changes the end-results. Running a deeper analysis (letting the computer calculate longer) will give a generally more reliable evaluation that is less likely to change as much. Even still a few rare positions chess computers still don't understand as well as human grandmasters, but that too could be a deeper conversation.
Here is something that may be useful; it is IM @DanielRensch talking about CAPS.
Nice response!
Thanks, CAPS is misinterpreted by many, so the least I can do is try and explain it...or have Danny do some of that for me