Who said Barry Bonds isn't a class act?
The way it works: it first gives each statistical measurement a weight in terms of how many runs it produces on average (example: a triple was about 1.1, a stolen base .34, caught stealing -.65, etc., with related measures for pitchers). Then, the player's runs from that year are compared against an average player, or "replacement level" player of that same year, to determine how many more runs this player produced. "Runs" is then tranlsated to "wins", so that by the time you consider the entire player's career, you have a measurment of how many more "wins" they brought to the teams they played for.
I can't find the chart right now, but comparing careers, Ruth crushes everyone. IIRC, he was the only person to break 100 "wins" in this measure. He also had the best single season every, but I don't remember that as well.
To be sure, Bonds will rightly go down as one of the all-time greats. I think that putting him in the top 10 ever is not unreasonable. But it's only in his dreams that he'll take down the Bambino.
As a friend of mine said, "Put me in something the size of a badminton court, and I'll break the home run record too."