The fx-991ES is a scientific calculator that was released by Casio circa 2004. It features Casio's Natural Textbook Display feature which refers to the input method of the calculator, allowing the user to input equations just as they look on a textbook. It has a multitude of unit converters and scientific constants built-in and features eight modes including a statistical mode and a programmer mode allowing for decimal, hexadecimal, binary and octal calculations to be done.
I own a single example of this calculator which is in working condition with the slide case.
This calculator is in very poor condition as the result of me using it daily for maths class. It has served me well and now enjoys a peaceful retirement. While it is not broken, the screen is very damaged and has a dead line in the middle. The buttons on this calculator are perfectly servicable. It is small and very pocketable as well.
Gallery of pictures for this calculator