Retro 15C vs Plus42
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
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.
Plus42
This advanced scientific calculator simulates the classic HP-42S RPN calculator with enhanced features. It offers algebraic expressions, unit conversions, directories for storage, a larger resizable display, financial functions, and 2D plotting with integral and root finding.
- HP-42S RPN calculator simulation
- Algebraic expressions
- Attached units and conversions
- Program and variable directories
- Resizable 8-row, 22-column display
- Time value of money and amortization
- 2D function plotting with zoom and pan
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Plus42 is an advanced scientific programmable calculator, based on Free42. Free42, in turn, is a complete re-implementation of the HP-42S scientific programmable RPN calculator, which was made from 1988 until 1995 by Hewlett-Packard. Free42 is a complete rewrite and contains no HP code whatsoever. Plus42 builds on Free42 and adds: Algebraic expressions modeled after those used on the HP-27S and HP-17B/19B; attached units and unit conversions modeled after those used on the HP-48/49/50 series; directories for more organized storage of programs and variables; a larger display, with 8 rows and 22 columns (131x64 pixels) by default, which the user may resize at will; time value of money and amortization schedules; and two-dimensional plotting of functions, with ability to zoom and pan, and find integrals and roots from points in the plot.
Screenshots
Verdict
The clearest difference is price: Retro 15C at Free against Plus42's $9.99. Retro 15C also leads on iOS requirement (8.0 vs 12.0). Plus42's advantage is rating (4.9 vs 4.3) and update cadence (weekly vs every 53 months). On ratings volume, ads, in-app purchases and monetization model 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
Retro 15C is free to download; Plus42 costs $9.99 up front. Neither carries in-app purchases, so what you see is what you pay.
Plus42 holds the better App Store score, 4.9 against 4.3. Both are backed by a comparable volume of ratings — 212 and 79 respectively. Written reviews point the same way: 76% of Retro 15C's written reviews are positive against 92% of Plus42's.
Retro 15C ships an update every 53 months, Plus42 weekly. The most recent releases landed on October 7, 2026 and October 13, 2026 respectively.
| Parameter | Retro 15C | Plus42 |
|---|---|---|
| Price | Free — better | $9.99 |
| Rating | 4.3 (212 ratings) | 4.9 (79 ratings) — better |
| Positive reviews | 76.1% of reviews | 92.3% of reviews — better |
| Number of ratings | 212 — better | 79 |
| Update frequency | Every 53 months | Weekly — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free | Free |
| Devices | iPhone, iPod | iPhone, iPad, iPod — better |
| Requires iOS | 8.0 — better | 12.0 |
| Further details — not scored | ||
| Size | 5 MB | 11 MB |
| Age rating | 4+ | 4+ |
| Developer | Greg Hewgill | Thomas Okken |
Customer experience
Retro 15C
Plus42
Bugs and requests
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
Plus42
Not enough reviews yet to summarise bugs or requests.
In-app purchases
Retro 15C
No in-app purchases
Plus42
No in-app purchases
