|RPN| Scientific Calculator vs HP
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
|RPN| Scientific Calculator
This calculator app uses Reverse Polish Notation for powerful calculations. It offers customizable color schemes, layouts, and online help, designed for flexibility and usability. All features are unlocked with a one-time purchase.
- Reverse Polish Notation (RPN)
- Viewable stack
- Selectable portrait/landscape layouts
- Customizable color schemes
- Online visual help
- No ads or in-app purchases
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|RPN| Scientific Calculator is a calculator which features a variety of color schemes and layouts. It utilizes Reverse Polish Notation, a viewable stack, selectable portrait and landscape layouts, online visual help and many more. The application is meant to be as flexible and powerful as possible, without sacrificing usability. |RPN| does not have ads, and never will, nor does it use in-app purchases. All functionality comes with the purchase. Here is a youtube playlist with some helpful videos: https://www.youtube.com/playlist?list=PLucgGVHO2sKhnnNf1gapHS4Zy7u69VGAs
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
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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 price: HP at Free against |RPN| Scientific Calculator's $0.99. HP also leads on rating (4.6 vs 2.3) and review sentiment (100% vs 60%). |RPN| Scientific Calculator's advantage is device support (4 vs 1). On update cadence, ads, in-app purchases and iOS requirement 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
HP is free to download; |RPN| Scientific Calculator costs $0.99 up front. Neither carries in-app purchases, so what you see is what you pay.
HP holds the better App Store score, 4.6 against 2.3. That said, the two scores are not equally well evidenced: HP has 62 ratings behind it against 3, so its average is the more settled of the two. Written reviews point the same way: 60% of |RPN| Scientific Calculator's written reviews are positive against 100% of HP's.
|RPN| Scientific Calculator ships an update fortnightly, HP every 11 days. The most recent releases landed on October 24, 2026 and October 30, 2026 respectively.
| Parameter | |RPN| Scientific Calculator | HP |
|---|---|---|
| Price | $0.99 | Free — better |
| Rating | 2.3 (3 ratings) | 4.6 (62 ratings) — better |
| Positive reviews | 60.0% of reviews | 100.0% of reviews — better |
| Number of ratings | 3 | 62 — better |
| Update frequency | Fortnightly | Every 11 days — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | Free — better |
| Devices | iPhone, iPad, iPod, Mac — better | iPhone |
| Requires iOS | 16 — better | 17.2 |
| Further details — not scored | ||
| Size | 2 MB | 2 MB |
| Age rating | 4+ | 4+ |
| Developer | Bradley Smith | Enrique Haro |
Customer experience
|RPN| Scientific Calculator
HP
In-app purchases
|RPN| Scientific Calculator
No in-app purchases
HP
No in-app purchases
