I really wonder what the business case for spending so much effort on such precision was. Who are the users who need such accuracy but are using android calculator?
Students learning about real numbers. Yes seriously.
Unlike software engineers who have already studied IEEE754 numbers, you can't expect a middle school student to know concepts like catastrophic cancellation. But a middle school student wants to poke around with trigonometric functions and pi to study their properties, but a true computer algebra system might not be available to them. They might not understand that a random calculator app doesn't behave correctly because it's not using the same kind of numbers discussed in their math class.
while phones are mostly a circus people do try to use them for serious things. For a program you make the calculations as accurate as the application requires. If you don't know what a tool will be used for you never really get to feel satisfied.
