I think this is backwards. A calculator app should be a simple thing. There's nothing undefined or novel about a calculator app. You can buy a much more capable physical calculator from Texas Instruments for less than $100 and I'm pretty sure the CPU in one of those is just an ant with some pen and paper.

You and I only think it's complex because we've become accustomed to everything being complex when it comes to writing software. That's my point. The mathematical operations are not hard (even the "fancy" ones like the trig functions). Formatting a number to be displayed is also not hard (again, those $100 calculators do it just fine). So, why is it so hard to write the world's 100,000th calculator app that the world's highest paid developers can't get it 100% perfect? There's something super wrong with our situation that it's even possible to have a race condition between the graphical effects and the actual math code that causes the calculator to display the wrong results.

If we weren't forced to build a skyscraper with Lego bricks, we might stand a better chance.