I've replaced the default ios calculator with a number of 3rd party alternatives, but after reading what bugs were fixed in a recent update of a calc app, I started wondering...how do you know that it's giving the correct output, especially if it's a more complex, scientific calulator? Same goes with unit-conversion apps. I consider having one on my phone to be a must. Maybe I wouldn't need one if the United States had adopted the metric system...as it is, I deal with measurements that trace their origins back to the width of an average sized Roman horse's ass. Soooo...how do I know the app is spitting out correct info? Any companies that are known for their accuracy?