Chess.com Game Report Calculations

[BrianErdelyi]

It may not be perfect, however, I like the idea of Chess.com's game report. I am trying to understand how some of the values are calculated. Any thoughts?

1. Accuracy. Possibly derived on something like (best+excellent moves)/(total moves excluding book)?
2. Move Ratings:
* Brilliant - This move not only was the best move but was difficult to find, even for the engine! Good job! 
* Best Move - The best move, according to the engine!
* Excellent - A great move, but not quite the best!
* Good - This move is okay, but could be better!
* Book -  An established opening move
* Inaccuracy - This is a weak move that could be much better
* Mistake - A bad move that immediately worsens your position
* Blunder - A very bad move that could lose material or lose the game
* Missed win - A move was missed that would have won material, or won the game

[Steve Maughan]

I've been impressed with Chess.com's game report. It has just the right amount of detail. It shows the highlights (and low-lights) and accuracy measure is a nice single-statistic measure of how well you played in general. It would be nice if a desktop GUI could generate such a report from any game.

Steve

[Henk]

I get the impression that the longer the game the higher the accuracy. If so they should change that.
Or maybe i'm an expert in playing end games. I doubt that.

I think middlegame has negative impact on accuracy.