Usability is a tough challenge and I especially like your clear explanations of how the calculations are done. Having tried it on iPhone, a specific UI feedbac

Usability is a tough challenge and I especially like your clear explanations of how the calculations are done. Having tried it on iPhone, a specific UI feedback I would have is making the page scrollable even when the numpad is displayed. I found myself typing the input, wondering where the output was, and not being able to scroll until I closed the numpad.