Numerical stability is but one of many desirable properties which should be considered when designing statistical software. However, rigorous roundoff analysis is rarely done because it seems not worth the price; the influence of rounding error is usually of secondary importance, and the analysis is thought to be beyond the reach of all but a few specialists. This note discusses the role of roundoff analysis in the design of a statistical program and shows that new techniques sometimes make assessment of the effect of rounding errors no more difficult than the verification of other program properties.