RPN 28x Calc 4+

Math can be fun‪.‬

tredje design

Designed for iPad

    • 5.0 • 1 Rating
    • $10.99



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.


- 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.

What’s New

Version 3.5.3

- Brings back the nice button titles, especially for the square root title, the A-Z title, and buttons with sigma or arrow characters.

Version 3.5:
- Adds scientific units & constants, double-tap a unit to add it to the stack.
- Unit conversion with CONVERT command.
- The log/variable/units viewer is now also on iPhone.
- Debugging programs: add breakpoints with HALT; use SST to step through the list of commands.
- Adds upper-tail probability distribution commands for the chi-square (UTPC), Snedecor's-F (UTPF), standard normal (UTPS), normal (UTPN), and Student's-T (UTPT) distributions.
And more; see version history.

Ratings and Reviews

5.0 out of 5
1 Rating

1 Rating

labmis101 ,

Awesome RPN app !!

Great app to replace my now not functioning m48+ emulator that let me going since my hp m48 went the way of the dodo.
Wonderfully supported app that offers great features including hms+ hms- etc in an easy to use interface that offers the flexibility of being a fully fledged iOS app and not just an emulator!!

MarvinMoose10 ,

Ahh, the memories

In the olden days I had an hp 28s. I loved it and it was a great calculator at the time. This isn't a bad reproduction, but please keep working on it.

App Privacy

The developer, tredje design, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer's privacy policy.

Data Not Collected

The developer does not collect any data from this app.

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  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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