HP 33s Scientific manual RPN The Automatic Memory Stack, What the Stack Is

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RPN: The Automatic

Memory Stack

This chapter explains how calculations take place in the automatic memory stack in RPN mode. You do not need to read and understand this material to use the calculator, but understanding the material will greatly enhance your use of the calculator, especially when programming.

In part 2, "Programming", you will learn how the stack can help you to manipulate and organize data for programs.

What the Stack Is

Automatic storage of intermediate results is the reason that the HP 33s easily processes complex calculations, and does so without parentheses. The key to automatic storage is the automatic, RPN memory stack.

HP's operating logic is based on an unambiguous, parentheses–freemathematical logic known as "Polish Notation," developed by the Polish logician Jan àukasiewicz (1878–1956).

While conventional algebraic notation places the operators between the relevant numbers or variables, àukasiewicz's notation places them before the numbers or variables. For optimal efficiency of the stack, we have modified that notation to specify the operators after the numbers. Hence the term Reverse Polish Notation, or RPN.

The stack consists of four storage locations, called registers, which are "stacked" on top of each other. These registers — labeled X, Y, Z, and T — store and manipulate four current numbers. The "oldest" number is stored in the T– (top) register. The stack is the work area for calculations.

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