(Of course, all this means that if you're more likely to multiply things together than add them, the badness of an approximation depends on the ratio between it and the true value rather than the difference, and things are distributed log-normally, you should use the geometric mean instead. Or just take the log of everything.)

(Of course, all this means that if you're more likely to multiply things together than add them, the badness of an approximation depends on the ratio between it and the true value rather than the difference, and things are distributed log-normally, you should use the geometric mean instead. Or just take the log of everything.)