HP vs Modern RPN
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
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)
Modern RPN
A minimalist reverse Polish notation calculator for iOS devices. It offers Standard, Binary, and Hex modes for quick calculations and programmer-friendly conversions, featuring a clean interface and a 4-level stack.
- Reverse Polish Notation (RPN) input
- Standard, Binary, and Hex modes
- 4-level visible stack
- Calculation history
- Saved session state
- Clean dark interface
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Modern RPN is a minimalist reverse polish notation calculator for iPhone and iPad, with Standard, Binary, and Hex modes for fast everyday math and programmer-friendly conversions. Use a clean 4-level stack, instant mode switching, calculation history, and saved session state to move quickly without clutter. Features: • True RPN input with ENTER to push or duplicate values • Standard, Binary, Financial, and Hex calculator modes • Mode-aware entry and display formatting • 4-level visible stack: T, Z, Y, X • Core operations: add, subtract, multiply, divide • Stack tools: POP, X/Y swap, sign toggle, backspace, and all clear • Calculation history with timestamps • History filtering by All, Standard, Binary, Financial, or Hex • Saved session state for your current mode, stack, and in-progress input • Clean dark interface designed for focus and readability • No accounts, no ads, no data collection Modern RPN is designed for people who want the speed of a classic RPN calculator with a modern iOS interface.
Screenshots
Verdict
The clearest difference is price: HP at Free against Modern RPN's $2.99. HP also leads on ratings volume (58 vs 1) and iOS requirement (17.2 vs 26.2). Modern RPN's advantage is rating (5.0 vs 4.6) and update cadence (every 5 days vs every 11 days). On review sentiment, ads, in-app purchases and device support 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; Modern RPN costs $2.99 up front. Neither carries in-app purchases, so what you see is what you pay.
Modern RPN holds the better App Store score, 5.0 against 4.6. That said, the two scores are not equally well evidenced: HP has 58 ratings behind it against 1, so its average is the more settled of the two. Written reviews split almost evenly too, at 100% and 100% positive.
HP ships an update every 11 days, Modern RPN every 5 days. The most recent releases landed on October 24, 2026 and October 25, 2026 respectively.
| Parameter | HP | Modern RPN |
|---|---|---|
| Price | Free — better | $2.99 |
| Rating | 4.6 (58 ratings) | 5.0 (1 ratings) — better |
| Positive reviews | 100.0% of reviews | 100.0% of reviews |
| Number of ratings | 58 — better | 1 |
| Update frequency | Every 11 days | Every 5 days — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free — better | Paid |
| Devices | iPhone | iPhone, iPad — better |
| Requires iOS | 17.2 — better | 26.2 |
| Further details — not scored | ||
| Size | 2 MB | 2 MB |
| Age rating | 4+ | 4+ |
| Developer | Enrique Haro | Kevin Flathers |
Customer experience
HP
Modern RPN
In-app purchases
HP
No in-app purchases
Modern RPN
No in-app purchases
