RPN 28x Calc vs DB50X
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
RPN 28x Calc
A programmable scientific calculator offering a classic aesthetic with modern functionality. It features a dynamic stack display, customizable buttons, and support for multiple data types, making complex calculations intuitive and accessible.
- Reverse Polish Notation (RPN) input
- Dynamic stack display with scrolling
- Customizable buttons and programming
- Support for multiple data types (real, complex, binary, lists, etc.)
- 147 scientific units and physical constants
- Interactive program debugging
- Units and log viewers
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RPN 28x Calc is a programmable scientific calculator with a pleasingly classic look. Despite its nostalgic appearance, it offers a modern and intuitive user experience, allowing you to interact with your operands by touching them in the display. It is a reverse-polish notation (RPN) calculator with a dynamic stack display. As you add more values to the stack, the display shown on an iPad automatically expands. To see more lines, simply swipe to scroll. You can also re-order the levels or modify any of the values on the stack. ----- "It’s the third RPN calculator I buy for my iPad 2 and the first that makes me happy. It’s graphically appealing, intuitive and very responsive. I rated it 5 stars." (Nuno Gomes) ----- Advanced commands are available in a secondary panel on iPad or as alternative button pages on iPhone. The buttons are efficiently grouped into five pages that you can quickly access by swiping left or right: - user-defined buttons, - letters A-Z for typing, - trigonometric, logarithmic, and data manipulation commands, - statistics, storage and programming commands - binary integers, system flags and boolean logic. This is why RPN 28x Calc is unique in its class: - You can tap a row to select it and issue commands for the selected level. - In REORD mode, it is possible to rearrange the stack by dragging the rows. - You can swipe up or down the display to see all levels. - When you enter a value, you can tap a digit to reposition the cursor. - Tap on the status indicators in the top of the display to change their state. - Drag buttons to re-arrange them as you like it (enable that in the settings). Additionally, on iPad: - The display automatically resizes to show more than just 4 levels of the stack. - You can slide the secondary panel out of view or swipe across the panel to navigate between button pages. New: - 147 scientific units and elementary physical constants. - Upper-tail probablity distribution commands. - Interactive program debugging. RPN 28x Calc is all you need. - High precision arithmetics. - Supports multiple data types: real numbers, complex numbers, binary integers, or lists, arrays, vectors, matrices, programs, names, and strings. - Name your own variables; inspect them in the variable viewer. - Use the rich command set to write your own programs. - Create buttons for your programs. - Interactive button reordering. - Browse all scientific units and constants in the units viewer. - View the command history and the results in the log viewer. - Customizable button click & alert volumes. - Support for landscape orientation. - Optional thousand separators. - Haptic feedback on iPhone. - External keyboard support. - Dark Appearance since iPadOS 13 or iOS 13. - Alternative, dark app icon. - Use the same app on iPad or iPhone. - Use the calculator in iPad multitasking, i.e. in a Slide Over view or in Split View. - No ads, no tracking, and no rating requests. - Downloadable user guide with introduction and command reference (PDF). ----- Plans for future versions (NOT YET SUPPORTED): - Arithmetic expressions.
DB50X
This scientific calculator offers high-precision computations with arbitrary precision for numbers. It supports advanced functions like complex numbers, matrices, symbolic calculations, and graphing, with a user-friendly interface and extensive built-in help.
- Arbitrary precision calculations
- RPN and algebraic operations
- Complex numbers, vectors, matrices
- Symbolic and numerical solving
- Graphing and plotting
- Engineering units and constants
- Unicode text support
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DB50X is a new high-precision scientific calculator inspired by the legendary HP50G series from Hewlett-Packard. It is not an emulator, but a redesign from scratch, which is faster, and delivers never seen before capabilities like computations in arbitrary precision. Like the original HP50G, DB48X supports an unlimited stack, RPN and algebraic operations, complex numbers, based numbers, vectors, matrices, text, symbolic computations, numerical solving and integration, graphing and plotting, statistics, engineering units, and well over 1000 built-in functions. It integrates a library of equations and constants covering mathematics, physics or chemistry. Using modern technologies, DB50X goes well beyond the original HP50G in many ways: - It is significantly faster, uses less memory, and features a higher-resolution 240x400 pixels graphical color display. - Integer and decimal values can have an arbitrarily large number of digits, so you can compute log(pi) with 200 digits in a few keystrokes. - The six function keys feature up to three function per key, giving quick access to up to 18 related functions at a time. - Complex numbers can mix and match polar and rectangular form. - Symbolic operations extend to complex numbers, vectors and matrices. - Based numbers can be in any base from 2 to 36, and support any number of bits, making it easy to emulate a 23-bit or 512-bit processor. - Text is represented using Unicode instead of the proprietary HP encoding, facilitating data exchange with the rest of the world. - Multiple graphs can be distinguished using colour patterns - Engineering units include all the modern evolutions of the SI system, and can be configured by the user, e.g. to integrate currency units with the exchange rate du jour. Converting between USD/hour and EUR/day has never been so easy! - A built-in hyperlinked help system documents functions simply by holding the corresponding key, and combine a quick start guide, a user manual and a reference manual. - Over 700K of memory is available for RPL programs. - Access to iCloud to save your program and edit them from your Mac. DB508X will run many user RPL programs designed for the HP48, HP49 or HP50 directly as is. However, since it is not an emulator, it will not run any HP binary object, and notably will not run HP50G games or anything involving system RPL. This is an early-access release. Please consult https://github.com/c3d/db48x/blob/stable/doc/5-Unimplemented.md for a list of commands that are not yet implemented. DB50X is part of a family of related calculators that include the black-and-white DB48X and the entry-level DB40X.
Screenshots
Verdict
The clearest difference is price: RPN 28x Calc at $6.99 against DB50X's $9.99. RPN 28x Calc also leads on ratings volume (34 vs 8) and iOS requirement (12.4 vs 14.0). DB50X's advantage is update cadence (every 3 weeks vs every 2 months). On rating, review sentiment, 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
RPN 28x Calc costs $6.99 and DB50X $9.99 up front. Neither carries in-app purchases, so what you see is what you pay.
On the App Store both sit at effectively the same score — 5.0 for RPN 28x Calc against 5.0 for DB50X. Both are backed by a comparable volume of ratings — 34 and 8 respectively. Written reviews are what separate them: 97% of RPN 28x Calc's written reviews are positive against 100% of DB50X's.
RPN 28x Calc ships an update every 2 months, DB50X every 3 weeks. The most recent releases landed on September 13, 2026 and September 7, 2026 respectively.
| Parameter | RPN 28x Calc | DB50X |
|---|---|---|
| Price | $6.99 — better | $9.99 |
| Rating | 5.0 (34 ratings) | 5.0 (8 ratings) |
| Positive reviews | 96.7% of reviews | 100.0% of reviews — better |
| Number of ratings | 34 — better | 8 |
| Update frequency | Every 2 months | Every 3 weeks — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | Paid |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 12.4 — better | 14.0 |
| Further details — not scored | ||
| Size | 3 MB | 7 MB |
| Age rating | 4+ | 4+ |
| Developer | tredje design | Christophe de Dinechin |
Customer experience
RPN 28x Calc
DB50X
In-app purchases
RPN 28x Calc
No in-app purchases
DB50X
No in-app purchases









