How computers get it wrong: 2+2 = 5
When lives depend on calculations, human error can kill. From the early days of computing, one problem has been that they generally work with a fixed number of digits, creating rounding errors. Chaos Theory has shown new ways in which computer arithmetic can give misleading results. Such problems are not just theoretical - legend has it that one programmer became rich transferring the fractions of a penny lost in rounding errors into his own account!