Simple mathematical problem, + and - only: >>> 1800.00-1041.00-555.74+530.74-794.95 -60.950000000000045 That's wrong. Proof http://www.wolframalpha.com/input/?i=1800.00-1041.00-555.74%2B530.74-794.95 -60.95 aka (-(1219/20)) Is there a reason Python math is only approximated? - Or is this a bug? Thanks for all info, Alec Taylor