# Willis15C — RPN Scientific Calculator

> RPN Scientific Calculator (iPhone/iPad app by Stacy Lacy.)

- Source: https://appshunter.io/ios/app/willis15c/id6830661574 (this page in markdown: same URL + `.md`)
- Developer: [Stacy Lacy](https://appshunter.io/developer/1838215615)
- Category: Utilities, Education
- Price: $3.99
- Age rating: 4+
- Requires: iOS 26.0 · 5 MB
- Languages: American English
- Released: 2026-11-06
- Data updated: 2026-11-11

## What is Willis15C?

Willis15C is a programmable RPN scientific calculator for people who think in Reverse Polish Notation and want to trust every digit.

It computes in 10-digit decimal arithmetic, not binary floating point, so 0.1 + 0.2 is 0.3. Results round the way a classic scientific calculator rounds, across the full range from 1e-99 to 9.999999999e99. The math engine has been checked against more than 20,000 independently computed cases.

A CLASSIC FACEPLATE A horizontal layout with a brushed-metal panel, dark bevelled keys, gold and blue shifted functions, and a seven-segment display with status indicators. Everything is drawn in code, so it stays sharp at any size. On iPhone it fills the screen in landscape.

SEE THE WHOLE STACK Slide out the stack panel to watch X, Y, Z, T, LAST X, and the storage registers update as you work, including the imaginary stack in complex mode.

ADVANCED TOOLS • Keystroke programming with labels, subroutines, loops, tests, and flags • SOLVE finds the roots of your own functions • Numerical integration of your own functions • Complex numbers, with functions that work on both parts • Matrices: up to five, with inverse, determinant, and solving linear systems • Statistics, linear regression, permutations, combinations, and random numbers • Hyperbolic functions, polar and rectangular conversion, and time and angle conversion • Built-in help, with worked examples for every part of the calculator

BUILT FOR THE KEYBOARD On Mac, type digits and operators directly, press Return for ENTER, and open an on-screen key map any time. Copy and paste the X value.

ALWAYS WHERE YOU LEFT IT Your stack, registers, programs, and settings are saved automatically, like continuous memory.

PRIVATE BY DESIGN No account, no ads, no tracking, and no internet connection needed. Nothing leaves your device.

## Is Willis15C safe?

Not enough ratings yet to assess Willis15C.

## Is Willis15C legit?

Willis15C appears legitimate, with a few gaps. The AppsHunter Legitimacy Score for Willis15C is 65 out of 100 points across 7 verification signals from App Store and developer data.


## Version history (last 1 release)

### 1.0 — 2026-11-06

No release notes.

## More apps by Stacy Lacy

- [WillisMD Pro](https://appshunter.io/ios/app/willismd-pro/id6752208822)
- [WillisGSD](https://appshunter.io/ios/app/willisgsd/id6757086506)
- [CardLoom](https://appshunter.io/ios/app/cardloom/id6780286118)
- [WillisLogger: Ham Radio Log](https://appshunter.io/ios/app/willislogger-ham-radio-log/id6787128648)
- [WillisTP - Teleprompter](https://appshunter.io/ios/app/willistp-teleprompter/id6789900273)
- [Lantern Bible App](https://appshunter.io/ios/app/lantern-bible-app/id6808736311)

All apps by Stacy Lacy: https://appshunter.io/developer/1838215615

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-11-11.*