Numbers first, then the operation
In Reverse Polish Notation you enter the operands and then press the operator, so there are no parentheses and no equals key. To work out 5 − (1 + 2), press
5ENTER1ENTER2+−
Each result waits on the stack for the next operation, and the display shows the stack as you go.
What it does
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A stack as deep as you need
ENTER pushes the number you typed, and a flick of the display reads every level of the stack.
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Undo and redo
UNDO steps the stack back one operation at a time, and REDO steps it forward again.
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26 registers
Store and recall in A to Z, or exchange x or y with any of them. They keep their values when you close the app.
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Scientific functions
Trigonometry in degrees or radians, hyperbolic functions, logarithms, factorials, combinations and permutations, polar coordinates, hours, minutes and seconds, and unit conversions.
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Complex numbers
Behind the CPLX prefix: arithmetic, squares and roots, powers, the exponential and logarithm, and trigonometry.
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Statistics
Enter pairs with Σ+ for their sums, means, weighted means, standard deviations, correlation and least-squares line.
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Fractions
Hold FDISP to see a result as a fraction, with a limit on the denominator that you set.
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Hexadecimal, octal and binary
32-bit two’s complement integers, with AND, OR and XOR and their negations, NOT, two’s complement and shifts.
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Display modes
Fixed, scientific and engineering notation at the precision you choose, a decimal point or comma, an optional thousands separator, and SHOW for more digits.
Keys where you expect them
The keyboard, its shifted functions and the menus follow the classic RPN scientific pocket calculators, so the keys are where you expect them. The stack has no fixed depth, so nothing falls off the top, and ENTER pushes the number being typed rather than copying it. RPN9 is a calculator, not a programmable one: it has no programs, equation solving or integration.
No account, no ads, no tracking
RPN9 has no account, no ads and no analytics, and it does not go online. The stack, the registers and the settings are kept on your phone so that you can pick up where you left off. The privacy policy has the details.