You enter your calculations in the input-region and when you select the 'Evaluate' action, you get the results in the output-region! There are quite a bit of functions together with the option to use a variables.

Update Description:
v1.1:
- Added a notation to enter numbers with commas as separators between thousands, where the commas are ignored. To do this, just put the number between single quotes. Example: '10,000,000'.
- Added documentation inside the application.
- Removed unnecessary user-interface elements, like the tabs, and empty menus.