> Another "niche" area is finance, insurance, taxes and anything nearby, fixed point in those area is, I hear, a must. Because all the usual invariants of high

> Another "niche" area is finance, insurance, taxes and anything nearby, fixed point in those area is, I hear, a must. Because all the usual invariants of high school algebra that FP breaks actually have significance. In particular, double-entry bookkeeping (standard practice for centuries) uses the accounting equation [1] as a checksum. If the two sides of the equation are ever unequal, then there's been a mistake somewhere that needs to be corrected. If you add the same value to a large asset account and a small liability account, for example, you can run into problems: The internal rounding performed by floating point arithmetic can mean that the increase to each side of the equation is slightly different, throwing the system out of balance. [1] https://en.wikipedia.org/wiki/Accounting_equation https://en.wikipedia.org/wiki/Accounting_equation