Usability problems

Application isnt really bad. It has a pretty look, quick response on user taps, history and so on. But what is definitely the problem about its use is the small sensitive areas around the digits on the key pad in vertical aspect while the numbers are too small. It takes user to concentrate too much to tap a humber precisely and to control the result of tapping via the edit line under display. Very often I tap a small digit and found a mistake in my calculations later because i didnt tap right into the very digit. It happens when i tap a little i. between of two digits in a column. Beautiful app with epic fail in usability.
What would be nice is to have sound clicks option.

Jashutin about Calzy, v2.0