Actually ‘AC’ clear all the calculation if pressed one time, and if pressed for the second time the display history is cleared. Google web calculator works in a similar way.
I’ll fix that approximation bug.
https://www.google.it/search?q=calculator
Google calculator doesn’t have a dedicated ‘AC’ button.
Maybe I can change the button to show ‘AC’ at first instance.
Thanks for the suggestion.
All bugs should be fixed now.