Section 3

The Automatic Memory Stack,

LAST X, and Data Storage

The Automatic Memory Stack

and Stack Manipulation

HP operating logic is based on a mathematical logic known as ―Polish Notation,‖ developed by the noted Polish logician Jan Łukasiewicz (Wookashye'veech) (1878-1956). Conventional algebraic notation places the algebraic operators between the relevant numbers or variables when evaluating algebraic expressions. Łukasiewicz’s notation specifies the operators before the variables. For optimal efficiency of calculator use, HP applied the convention of specifying (entering) the operators after specifying (entering) the variable(s). Hence the term "Reverse Polish Notation" (RPN).

The HP-15C uses RPN to solve complicated calculations in a straightforward manner, without parentheses or punctuation. It does so by automatically retaining and returning intermediate results. This system is implemented through the automatic memory stack and the v key, minimizing total keystrokes.

The AutomaticMemory Stack RegistersT0.0000 Z 0.0000 Y 0.0000X 0.0000 Always displayed

When the HP-15C is in Run mode (no PRGM annunciator displayed), the number that appears in the display is the number in the X-register.

32