It can add, subtract, multiply, and divide any two numbers, and show you the result as long as it's not too long. If it has more than eight digits, it will show an E. Same thing if your number is less than -99999999. And if you divide, and your result has too many decimal digits, it'll will show another E. (Don't be afraid to try big numbers!) Note to all: You may run into a few bugs, like if you do 69 divided by 4 for example. Don't think it's a bug if it says E----1725. I checked it by downloading, and it said the right answer- 17.25. But you can still use it online if you don't mind.
Thanks to @Chrischb for the original project