Hi, There is a mistake is logBase: $ ghci GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. Prelude> logBase 10 10 1.0 Prelude> logBase 10 100 2.0 Prelude> logBase 10 1000 2.9999999999999996 <--- eeeerrgghhhh! Prelude> logBase 10 10000 4.0 My host is a Debian GNU/Linux 5.0.2 (lenny) with the following GHC packages: ii ghc6 6.10.4-1 ii ghc6-doc 6.10.4-1 ii libghc6-mtl-dev 1.1.0.2-7+b1 ii libghc6-utf8-string-dev 0.3.5-1+b1 ii libghc6-x11-dev 1.4.5-6 rc libghc6-x11-doc 1.4.2-1 ii libghc6-x11-xft-dev 0.3-3+b3 ii libghc6-xmonad-contrib-dev 0.8.1-3+b3 rc libghc6-xmonad-contrib-doc 0.8-2 ii libghc6-xmonad-dev 0.8.1-5 Regards!