I suppose I'm looking for a Dick and Jane guide. I've only tested one value and I should test boundary conditions, but I feel I should also be trying to break it in other ways and look at the results. Looking at it right now, there's no validity checking on the input. I only feed it numbers, but there would be nothing stopping someone from feeding it characters. Well, perhaps that's the Right Thing to do, instead of restricting someone else's use of the code. It comes down to the difference between broken code and "creative" use yielding unexpected results.