Free42 vs Retro 15C
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Free42
This application is a faithful re-implementation of the HP-42S scientific calculator and its associated printer. It offers full functionality without requiring original HP ROM images and is an open-source project.
- HP-42S calculator simulation
- HP-82240 printer simulation
- Open source project
- No HP ROM required
- Complete rewrite
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Free42 is a re-implementation of the HP-42S calculator and the HP-82240 printer. It is a complete rewrite, not using any HP code, and it does not require an HP-42S ROM image. Free42 is an Open Source project. The executables and source code are released under the terms of the GNU General Public License, version 2. All third-party code used in Free42 is either in the public domain, or licensed under terms compatible with GPLv2, or used with the authors' permission.
Retro 15C
This app emulates a classic RPN scientific calculator, offering advanced features like complex number arithmetic, matrix calculations, and programmability. It provides a functional and complex tool reminiscent of 1980s calculators.
- Complex number arithmetic
- Matrix calculations
- Numerical root finder
- Numerical integration
- Statistical functions
- Programmable
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Students and scientists from the 1980s will remember the classic RPN scientific calculators. These calculators strike a perfect balance between functionality and complexity. * Complex number arithmetic and trig functions * Matrix calculations * Numerical root finder * Numerical integration * Statistical functions, linear regression * Fully programmable This app is completely free, no ads or extra bits to buy. I love this calculator and I like to share.
Screenshots
Verdict
The clearest difference is rating: Free42 at 4.8 against Retro 15C's 4.3. Free42 also leads on update cadence (every 9 days vs every 53 months) and review sentiment (94% vs 76%). Retro 15C's advantage is iOS requirement (8.0 vs 15.0). On price, ratings volume, ads and in-app purchases there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
Free42 holds the better App Store score, 4.8 against 4.3. Both are backed by a comparable volume of ratings — 287 and 233 respectively. Written reviews point the same way: 94% of Free42's written reviews are positive against 76% of Retro 15C's.
Free42 ships an update every 9 days, Retro 15C every 53 months. Both last shipped on October 26, 2026.
| Parameter | Free42 | Retro 15C |
|---|---|---|
| Price | Free | Free |
| Rating | 4.8 (287 ratings) — better | 4.3 (233 ratings) |
| Positive reviews | 94.4% of reviews — better | 76.1% of reviews |
| Number of ratings | 287 — better | 233 |
| Update frequency | Every 9 days — better | Every 53 months |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free | Free |
| Devices | iPhone, iPad, iPod — better | iPhone, iPod |
| Requires iOS | 15.0 | 8.0 — better |
| Further details — not scored | ||
| Size | 9 MB | 5 MB |
| Age rating | 4+ | 4+ |
| Developer | Thomas Okken | Greg Hewgill |
Customer experience
Free42
Retro 15C
User reviews
Free42
From 287 App Store ratingsWhat we love
- 🚀 Faithful reproduction of HP42S
- 👍 Identical to physical calculator
- 👍 Runs all original programs
- 👍 Convenient to have on phone
- 👍 Haptic feedback on button presses
Room to improve
- 🐛 Screen not filling entire display on newer devices
- 🔇 Configurable key click sound missing
- 🔇 Lack of loud click sound feedback
Retro 15C
From 233 App Store ratingsWhat we love
- 🚀 Lightning-fast calculator
- 👍 Authentic look and feel of HP 15C
- 🚀 Faster than real HP 15C
- 👍 Excellent RPN emulation
- 👍 Familiar interface for HP 15C users
Room to improve
- 🐛 Doesn't save settings, programs, or memory
- 🐛 No key press feedback or sound
- 🐛 Blinking display issue with large calculations
- 🐛 Bugs with HMS conversions
- 🐛 Can't close app on newer iPhones
Bugs and requests
Free42
Reported bugs
2 issues- Occasional issues with Solver function
- Store and Recall functions not working properly
Requested features
3 requests- Display all registers (X, Y, Z, T, Last X) simultaneously
- Ability to share/transfer programs between devices
- Improved use of screen real estate on larger displays
Retro 15C
Reported bugs
4 issues- Blinking display with large calculations
- Bugs with HMS conversions
- Inability to close app on newer iPhones
- Stopped working with iOS 14 updates
Requested features
5 requests- Add haptic feedback on key presses
- Implement continuous memory to save settings and programs
- Add portrait mode option
- Improve compatibility with newer iOS versions
- Add copy/paste functionality for stack and registers
In-app purchases
Free42
No in-app purchases
Retro 15C
No in-app purchases
