How to reset calculator on Mac Book air

Hi:

I have a Mac Book Air. I were using the calculator and pressed a green button with a + sign on it, the button was beside two other buttons, a red one that close the calculator and an another orange button that minimizes the calculator.

When I pressed the green button, my calculator got many another symbols and functions, it has been more advanced.

How do I get it normal (standard)

Really thankful for help!!