As you learned in chapter 1, many development projects involve taking financial or statistical models that are specified in some other way (such as Microsoft Excel or MathWorks’ MATLAB) and translating them into robust, scalable systems. This task can be arduous. This chapter is a detailed case study of how my colleagues and I used F# to solve a problem we encountered during this process. I could’ve chosen from many other examples from the same project, which involved a substantial F# calculation engine. But we went up several blind alleys to solve this one, and that gives me the opportunity to show you how a feature can be brought to market promptly using an experiment-and-fail-fast approach—something at which F# excels.