RPN Calculator | Stack Replay, Memory Profiles & Precision

Quick Start Guide

  1. Enter your first number: Type a number, then press Enter to push it onto the stack.
  2. Enter your next number and an operator: The operator applies to the top two stack values and pushes the result back.
  3. Chain more operations: Keep entering numbers and operators — no parentheses or equals sign needed.
  4. Use stack functions: Swap, Roll ↓/↑, Drop, or Last X to manipulate the stack without retyping.
  5. Store values in memory: STO/RCL/SUM/SUB, with named memory profiles you can switch per project or client.
  6. Set precision and notation: Choose Auto, Fixed, Scientific, or Engineering notation.
  7. Review your history: Replay steps through the stack state before and after each operation.

Understanding RPN (Reverse Polish Notation)

How the stack works

Pressing Enter pushes the number you just typed onto the stack. An operator (+, -, ×, ÷) then pops the top two values, applies the operation, and pushes the result back — that is why RPN never needs parentheses or an equals sign.

Stack manipulation: Swap, Roll, Drop, Last X

Swap exchanges the top two stack values, Roll ↓/↑ cycles values through the stack without changing them, and Drop removes the top value entirely. Last X restores the value that was just consumed by the previous operation, useful for correcting a mistaken calculation without retyping.

Memory registers and profiles

STO stores the current value in memory, RCL recalls it, and SUM/SUB add or subtract from it. Memory profiles let you name and switch between separate register sets — for example one per project or client — without losing the active stack.

Precision and notation modes

Choose Auto, Fixed, Scientific, or Engineering notation and set the number of digits shown. Engineering notation keeps exponents in multiples of three, which lines up with common unit prefixes (kilo, mega, milli) for engineering work.

History replay

Every calculation is saved to history. Replay steps through the stack state before and after each operation, which is useful for auditing a multi-step calculation or picking up a result partway through.

Features

Exponential Keys: e^x and 10^x sit beside ln and log, so logarithms invert instead of being one-way.

Stack-Based Entry: Enter numbers then operators — no parentheses or equals sign needed.

Stack Functions: Swap, Roll ↓/↑, Drop, and Last X for correcting or manipulating without retyping.

Named Memory Profiles: Store separate register sets (STO/RCL/SUM/SUB) per project or client.

Precision Controls: Auto, Fixed, Scientific, or Engineering notation with adjustable digits.

Angle Modes: Switch the trig keys between degrees, radians and gradians, the way every RPN machine has since the HP-35.

Operation Replay: Step through stack state before and after each calculation in history.

Searchable History: Filter a long session by operation or result — and the export follows what you filtered.

Frequently Asked Questions

Yes. The Search History box above the list filters a long session by operation or result, so you can find the line you want without scrolling — type sin to see only the trig steps, or part of a number to find where it came from. Exporting while a search is active exports what you are looking at, and the operation count in the export reflects the filtered list rather than the whole session.
Yes. The DEG / RAD / GRAD control sits in the calculator header and applies to every trigonometric key, both forward and inverse: in radian mode ASIN returns radians, and in gradian mode it returns gradians. The setting is saved with the tab, so a workspace you come back to is still in the mode you left it in. Degrees is the default, which is what the calculator did before the control existed.
It works the same way. Reverse Polish Notation is the entry method Hewlett-Packard made standard on calculators like the HP-12C and HP-35: you enter the numbers first, then the operator, and the stack holds the intermediate results. If you learned RPN on an HP, the keystrokes here will feel familiar — Enter pushes a value onto the stack, and an operator consumes the top two.
RPN — also called postfix notation — is a mathematical notation where operators follow their operands. Instead of '2 + 2', you type '2 Enter 2 +'. It eliminates the need for parentheses and equal signs, making complex calculations faster and more efficient.
The stack stores your numbers. Each time you press Enter, the number is pushed onto the stack. Operations (like +, -, ×, ÷) take the top two numbers, perform the calculation, and push the result back. Use 'Swap' to exchange the top two numbers.
RPN calculators are often faster for complex calculations because you never need parentheses or an equals sign. Many engineers, scientists, and financial professionals prefer RPN for its efficiency and reduced keystrokes.
Yes. History view includes operation replay, so you can step through stack transitions and inspect before/after states. You can also push prior results back to the stack.
You can choose Auto, Fixed, Scientific, or Engineering notation and set precision digits. This is useful for engineering and repeatable workflow formatting.
Yes. Memory profiles let you name and switch register sets (for example, per project or per client) without losing the active session stack.

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