Past vs. Present
Not sure, but they probably look at some famous games by the players and the computer analysis finds the player's overall rating by identifying the accuracy of the moves or something.
This is the way I look at it - in the past there was no one rated 2700. Simply game of chess hasn't evolved to that level. People at the top were still beasts and can't be compared to todays standards. Same goes for our generation. Maybe in 200 years there will be much more players rated 2800+. There is nothing we can do about that. But to say someone else wasn't that good because we compared him with something new that didn't even exist when he was playins is wrong in my eyes.
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