It is simple but it can to calculate instance and able to visualize all process of calculation like child math book..
1. Visualize all process of calculation, just input and click on '=' button.
2. Support back button ( click on back button to return)
3. Mission button are indicated by different color.
4. Show massage for some mistake or clearing data.
5. Support Instance calculation with input new digit or delete any digit.
6. Support multiple operation for both mode
7. Nice animation with pressing back button or '=' button.
8. After completing all task, it can be exit by simply click on Exit button.