レートについて

計算式を解明しようと思ってProblem 0632の結果を取得したのがこちら。

[{"0":"mas","username":"mas","1":"14","length":"14","2":"566.371681416","point":"566.371681416","3":"2011-07-12 21:17:11","submissiontime":"2011-07-12 21:17:11","rank":1},{"0":"pasta","username":"pasta","1":"16","length":"16","2":"433.628318584","point":"433.628318584","3":"2011-07-12 21:11:04","submissiontime":"2011-07-12 21:11:04","rank":2}]

ちっとも分かりません。

追記
複数データに対して検証したところ、masさんの計算式で合っていました。