Retro 15C vs HP
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
Read full descriptionHide full description
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.
HP
Emulates classic Hewlett Packard RPN scientific calculators from the 1970s. Experience the original HP-35, HP-45, and HP-21 models on your iPhone.
- RPN calculator emulation
- HP-35 model
- HP-45 model
- HP-21 model
- Classic scientific calculator interface
Read full descriptionHide full description
The classic Hewlett Packard RPN (Reverse Polish Notation) calculators. - HP-35, HP-45. First pocket scientific calculators (1972). - HP-21. 2nd gen of the HP-35 (1975)
Screenshots
Verdict
The clearest difference is rating: HP at 5.0 against Retro 15C's 4.3. HP also leads on update cadence (every 11 days vs every 53 months) and review sentiment (100% vs 76%). Retro 15C's advantage is ratings volume (212 vs 5) and iOS requirement (8.0 vs 17.2). On price, 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
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
HP holds the better App Store score, 5.0 against 4.3. That said, the two scores are not equally well evidenced: Retro 15C has 212 ratings behind it against 5, so its average is the more settled of the two. Written reviews point the same way: 76% of Retro 15C's written reviews are positive against 100% of HP's.
Retro 15C ships an update every 53 months, HP every 11 days. The most recent releases landed on October 15, 2026 and October 8, 2026 respectively.
| Parameter | Retro 15C | HP |
|---|---|---|
| Price | Free | Free |
| Rating | 4.3 (212 ratings) | 5.0 (5 ratings) — better |
| Positive reviews | 76.1% of reviews | 100.0% of reviews — better |
| Number of ratings | 212 — better | 5 |
| Update frequency | Every 53 months | Every 11 days — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free | Free |
| Devices | iPhone, iPod — better | iPhone |
| Requires iOS | 8.0 — better | 17.2 |
| Further details — not scored | ||
| Size | 5 MB | 2 MB |
| Age rating | 4+ | 4+ |
| Developer | Greg Hewgill | Enrique Haro |
Customer experience
Retro 15C
HP
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
HP
Not enough reviews yet to summarise bugs or requests.
In-app purchases
Retro 15C
No in-app purchases
HP
No in-app purchases
