is that a Chessmetrics rating takes into account the frequency of play. According to Sonas, "As soon as you go a month without playing, your Chessmetrics rating will start to drop." Sonas, like Elo, claims that it is impossible to compare the strength of players from different eras, saying: Nevertheless, Sonas' website does compare players from different eras. Including data until December 2004, the ratings were: In 2005, Sonas used Chessmetrics to evaluate historical annual performance ratings and came to the conclusion that Kasparov was dominant for the most years, followed by Karpov and Lasker. He also published the following list of the highest ratings ever attained according to calculations done at the start of each month: {| class="wikitable sortable" style="font-size:100%;" !Rank !Rating !Player |- | align=center | 1 | align=center | 2895 | Bobby Fischer |- | align=center | 2 | align=center | 2886 | Garry Kasparov |- | align=center | 3 | align=center | 2885 | Mikhail Botvinnik |- | align=center | 4 | align=center | 2878 | Emanuel Lasker |- | align=center | 5 | align=center | 2877 | José Capablanca |- | align=center | 6 | align=center | 2860 | Alexander Alekhine |- | align=center | 7 | align=center | 2848 | Anatoly Karpov |- | align=center | 8 | align=center | 2833 | Viswanathan Anand |- | align=center | 9 | align=center | 2826 | Vladimir Kramnik |- | align=center | 10 | align=center | 2826 | Wilhelm Steinitz |} Warriors of the Mind In contrast to Elo and Sonas's systems, Raymond Keene and Nathan Divinsky's book Warriors of the Mind attempts to establish a rating system claiming to compare directly the strength of players active in different eras, and so determine the strongest player of all time (through December 2004). Considering games played between sixty-four of the strongest players in history, they came up with the following top ten: Garry Kasparov, 3096 Anatoly Karpov, 2876 Bobby Fischer, 2690 Mikhail Botvinnik, 2616 José Raúl Capablanca, 2552 Emanuel Lasker, 2550 Viktor Korchnoi, 2535 Boris Spassky, 2480 Vasily Smyslov, 2413 Tigran Petrosian, 2363 These "Divinsky numbers" are not on the same scale as Elo ratings (the last person on the list, Johannes Zukertort, has a Divinsky number of 873, which would be a beginner-level Elo rating). Keene and Divinsky's system has met with limited acceptance, and Warriors of the Mind has been accused of arbitrarily selecting players