Multiple difficulty levels 

Choose between 4 difficulty level, from the easiest one - with one digits-number - to the most difficult one* - with four digits-number.

* May required paid-for Premium access

As easy as writing on paper 

Use a calculator-like keyboard.  And get hints on where the next digit should be entered.  The result?  Exactly how writing on paper.

Step by step calculations 

Let the app split the calculation in easy to perform chunks - and then see how they will roll up in the main calculation.