editable history - Calculator app for iPhone and iPad

This is a simple calculator which has history function.
This calculators functions are as follows.

[main functions]
1. can display the history of input results.
2. can reuse a number on history by tapping it.
(When you reuse, a number underlined will be inputted.)
3. can edit a number on history and recalc all results on history.
(If you want to switch to edit mode, you push icon at the upper left.)

[tool functions]
1. square
2. root
3. change number size on history
4. change symboles (point and separator)
( [1,234.5] [1.234,5] [1 234,5] [1234.5])
5. set image on background (release by pushing long)
6. undo (When you want to cancel undo, you push undo button long.)

This calculator can reinput and reuse a number on history (input number and result) by tapping.
If you edit number on history, numbers and results on history will be recalced.

[use scene]
When you hava a dinner with friends, you decide to split the bill.
You calculate total amount and pay per person by the number of persons.
After that, you realize mistake that calculation and you have to recalc.
So far you have to reinput and recalc to get new result, but if you use this calculator, you easily can get new result only editing a number on history.

Please try this calculator.
If you have some suggestion, please contact me.