Reuben Fine, writing in 1976, observed that Botvinnik was at or near the top of the chess world for thirty years—from 1933, when he drew a match against Flohr, to 1963, when he lost the world championship for the final time, to Petrosian—"a feat equaled historically only by Emanuel Lasker and Wilhelm Steinitz". The statistical rating system used in Raymond Keene and Nathan Divinsky's book "Warriors of the Mind" concludes that Botvinnik was the fourth strongest player of all time: behind Garry Kasparov, Anatoly Karpov and Bobby Fischer but ahead of José Raúl Capablanca, Lasker, Viktor Korchnoi, Boris Spassky, Vasily Smyslov and Tigran Petrosian. The Chessmetrics system is sensitive to the length of the periods being compared but places Botvinnik third in a comparison of players' best individual years (1946 for Botvinnik) and sixth in a comparison of fifteen-year periods (1935–1949 in Botvinnik's case). In 2005, Chessmetrics' creator Jeff Sonas wrote an article which examined various ways of comparing the strength of "world number one" players, some not based on Chessmetrics; and Botvinnik generally emerged as one of the top six (the greatest exceptions were in criteria related to tournament results). FIDE did not adopt the Elo rating system until 1970, by which time Botvinnik's strength had been declining for several years. According to unofficial calculations by Árpád Elo, Botvinnik was the highest-rated player from 1937 to 1954, peaking about 2730 in 1946.