Comparison

i41CX+ vs RPN 28x Calc

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

i41CX+

This advanced RPN scientific calculator offers workstation-class Computer Algebra System (CAS) capabilities, going beyond traditional replicas. It provides access to an extensive library of modules and programs, enhanced with iOS features, customizable skins, and iCloud support for seamless data management.

Highlights
  • RPN logic with 4-element stack
  • Extensive memory registers
  • Over 400 built-in functions
  • Computer Algebra System (CAS)
  • Virtual thermal printer/plotter
  • Access to HP-41 module library
  • Customizable skins and keyboard overlays
Read full description

i41CX+ is an advanced programmable and expandable RPN scientific calculator with a virtual thermal printer/plotter and workstation-class CAS capabilities that is far beyond a mere replica of the original. In addition to being functionally equivalent to the world-renowned HP-41CX and providing access to its entire library of modules and programs, i41CX+ is enhanced with iOS and hardware features, keyboard overlays, rich set of import and export capabilities, traditional and upbeat diverse set of skins, complete color control, iCloud support, and much more. The i41CX+ CAS is a full implementation of REDUCE. It's like having Mathematica or the computational engine of Wolfram Alpha in your pocket and, best of all, it runs natively so no internet connection is required. The CAS is fully programmable and provides the ability to reuse previous results in computations. Moreover, the CAS has full access to the calculator registers so it is possible to combine RPN programs with CAS programs. This is the finest and most powerful scientific/engineering/financial calculator for iOS devices bar none. CALCULATOR FEATURES: • RPN logic with a 4 element deep memory stack • 319 main and 600 extended memory registers • Over 400 built-in functions, including over 100 functions created specifically for i41CX+ • Time, calendar, alarm, and stopwatch functions • Four module ports provide access to HP-41 expansion pacs • Rich set of functions and algorithms: numerical, mathematical, statistical, complex, matrix, numerical integration, curve fitting, solutions to equations, and much more • Powerful, flexible, and programmable Computer Algebra System (CAS) supporting symbolic, arbitrary precision, scalar, vector and matrix algebra calculations, 2D/3D plotting, and much more • Full-screen text editor with configurable font style and size, color scheme, a user configurable macro keyboard, and a numerical keyboard • Access to the entire HP-41 library of solutions for science, mathematics, statistics, engineering, business, financial, surveying, medicine, real estate, and many other domains • Programmable - virtually unlimited number of lines • User definable keyboard • Ability to operate the calculator using a Bluetooth keyboard • Device integration: external display mirroring, copy and paste, in-app mail, system keyboard, GPS, accelerometer, digital compass, time and date synchronization, AirPrint, and much more • Virtually unlimited data and program storage capacity using the device's flash memory for local storage • Import/export data, programs, overlays, modules, etc. via the web, email, and iTunes file sharing • iCloud syncing of files and preference settings • iOS 8 Notification Center widget • 43 available keyboard overlays and support for user created overlays • Sound support including synthetic tones and interface sounds • Support for calculator skins and optional mini stack display • Adjustable calculator speed, sound volume, and display colors • Usage & Examples table with usage tips and examples • Quick Reference Guide of all built-in functions • CAS Quick Reference with all built-in functions, operators, switches, and packages • Beautiful and clean user interface PRINTER FEATURES: • Support for printing, plotting, graphics, and special characters • User configurable and programmable print color • Export printer output via email, clipboard, or AirPrint • Ability to save a JPEG image of the paper roll to the device's photo album *********************************************************** A comprehensive FAQ and Mini-Manual are available at http://alsoftiphone.com/i41CXplus. Please don't hesitate to use the "Contact Us" link there if you cannot find the answers or information that you seek. Thank you.

About

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.

Highlights
  • 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
Features
Read full description

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.

Screenshots

i41CX+4 screens
RPN 28x Calc4 screens

Verdict

The call

The clearest difference is price: RPN 28x Calc at $6.99 against i41CX+'s $24.99. RPN 28x Calc also leads on rating (5.0 vs 4.8). i41CX+'s advantage is ratings volume (106 vs 34). On review sentiment, update cadence, 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

CostPrice · In-app purchases · Ads · Monetization

i41CX+ costs $24.99 and RPN 28x Calc $6.99 up front. Neither carries in-app purchases, so what you see is what you pay.

ReceptionRating · Positive reviews · Number of ratings

RPN 28x Calc holds the better App Store score, 5.0 against 4.8. Both are backed by a comparable volume of ratings — 106 and 34 respectively. Written reviews point the same way: 91% of i41CX+'s written reviews are positive against 97% of RPN 28x Calc's.

UpkeepUpdate frequency

i41CX+ ships an update every 5 weeks, RPN 28x Calc every 2 months. The most recent releases landed on September 23, 2026 and September 13, 2026 respectively.

Scorecard3 real differences · 7 level
i41CX+ versus RPN 28x Calc: the parameters behind the verdict, then further details
Parameteri41CX+RPN 28x Calc
Price$24.99$6.99 — better
Rating4.8 (106 ratings)5.0 (34 ratings) — better
Positive reviews91.3% of reviews96.7% of reviews — better
Number of ratings106 — better34
Update frequencyEvery 5 weeks — betterEvery 2 months
AdsNoNo
In-app purchasesNoNo
MonetizationPaidPaid
DevicesiPhone, iPad, iPodiPhone, iPad, iPod
Requires iOS13.012.4 — better
Further details — not scored
Size123 MB3 MB
Age rating4+4+
DeveloperAntonio Laganatredje design

Customer experience

i41CX+

All ratings106 ratings
Positive94.3%
Neutral0.9%
Negative4.7%
Written reviews265 reviews
Positive91.3%
Neutral3.0%
Negative5.7%

RPN 28x Calc

All ratings34 ratings
Positive100.0%
Neutral0.0%
Negative0.0%
Written reviews30 reviews
Positive96.7%
Neutral0.0%
Negative3.3%

Bugs and requests

i41CX+

Reported bugs

2 issues
  • Issues with the 41Z math module producing garbled output
  • Scaling problems with overlays

Requested features

4 requests
  • Landscape mode for better button size
  • Haptic feedback for button presses
  • Ability to load and save programs/modules via cloud/email
  • Macros or scripting support

RPN 28x Calc

Not enough reviews yet to summarise bugs or requests.

In-app purchases

None

i41CX+

No in-app purchases

None

RPN 28x Calc

No in-app purchases

Questions

Is i41CX+ free?
i41CX+ costs $24.99, with no in-app purchases.
Is RPN 28x Calc free?
RPN 28x Calc costs $6.99, with no in-app purchases.
Which has better reviews, i41CX+ or RPN 28x Calc?
RPN 28x Calc is rated higher. i41CX+ averages 4.8 out of 5 from 106 ratings, while RPN 28x Calc averages 5.0 from 34 ratings.
Do i41CX+ or RPN 28x Calc have ads?
Neither i41CX+ nor RPN 28x Calc shows ads.
Which is updated more often, i41CX+ or RPN 28x Calc?
i41CX+ ships an update every 5 weeks, and RPN 28x Calc every 2 months. Most recently, i41CX+ was updated on September 23, 2026 and RPN 28x Calc on September 13, 2026.

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