RPN Calc vs Halcyon Calc
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
RPN Calc
This app provides a straightforward reverse Polish notation (RPN) calculator experience, inspired by classic HP models. It offers a clean interface with large buttons for quick calculations on iPhone, iPad, and Apple Watch, along with a convenient Today Extension for immediate access.
- Reverse Polish Notation (RPN) input
- Clean, simple interface
- Large, easy-to-press buttons
- iPhone, iPad, and Apple Watch support
- Today Extension for quick access
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A simple reverse polish notation calculator loosely based on my trusty HP-32SII that runs on iPhone, iPad, and Apple Watch! If you are familiar with HP RPN calculators, the operation of this calculator should seem very straightforward - albeit simplified. It can't be programmed, and it doesn't handle binary, or hexadecimal numbers. But, it has a clean, simple interface with large, easy to press buttons. It has all of the functions required for quick calculations when your iPhone is handier than your computer or calculator. And, remember those cool calculator watches from the 1980s? Unfortunately, none of them were RPN. RPN Calc brings a reverse polish notation watch calculator to the Apple Watch! In addition to the standard RPN Calculator app that runs on iPhone, iPad, and Apple Watch, RPN Calc includes a handy micro RPN Calc Today Extension available for convenient access to quick calculations from the pull down Today screen.
Halcyon Calc
A powerful calculator app for students, engineers, and scientists. It handles complex numbers, symbolic expressions, unit conversions, and matrix operations, with advanced plotting and programming capabilities.
- Complex number calculations
- Symbolic expression manipulation
- Unit conversion with custom units
- Matrix and vector operations
- Symbolic plotting
- Programming of custom operations
- Statistical data analysis
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For students, engineers, scientists or people who fondly remember classic calculators, Halcyon Calc is a great application for manipulating numbers and even symbolic expressions. Features: - Use this calculator on an iPhone, iPod Touch or an iPad - Use your finger to quickly scroll through the stack to review intermediate results - Copy and paste support - Over 225 built-in operations, including trig, logarithms, real functions, complex operations and more - Allows you to work with real, complex and integer numbers. - Real and complex numbers can be displayed in standard, fixed, scientific and engineering format - Use over 120 built-in units to perform unit conversion or create your own units if the one you want is not already there - Integer numbers can be displayed in decimal, hexadecimal, octal and binary bases - Work with real and complex matrices and vectors. - Enter symbolic expressions and solve them for different values. Even better, solve quadratic formulas, collect and expand factors and terms, find minima, maxima and roots of any expression. - Plot symbolic expressions in X/Y coordinates. Pan the coordinate space by dragging the plot in any direction. Zoom in and out using a pinch gesture. - Determine symbolic derivative, taylor series or numeric integral of an expression. - Store numbers, lists, strings and expressions in symbols. Create hierarchies of symbols to allow you to organize your calculations. - Create sequences of calculator commands into programs, creating your own operations which you can then include in expressions. - Store statistical data and calculate totals, averages, standard deviations, linear regressions, etc over that data. - Calculate the probabilities associated with standard distributions like the normal, F and T distributions.
Screenshots
Verdict
The clearest difference is review sentiment: Halcyon Calc at 100% against RPN Calc's 34%. Halcyon Calc also leads on rating (4.9 vs 4.0) and ratings volume (18 vs 6). RPN Calc's advantage is price ($0.99 vs $4.99). On update cadence, 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
RPN Calc costs $0.99 and Halcyon Calc $4.99 up front. Neither carries in-app purchases, so what you see is what you pay.
Halcyon Calc holds the better App Store score, 4.9 against 4.0. Both are backed by a comparable volume of ratings — 6 and 18 respectively. Written reviews point the same way: 34% of RPN Calc's written reviews are positive against 100% of Halcyon Calc's.
RPN Calc ships an update every 3 months, Halcyon Calc every 4 months. The most recent releases landed on November 8, 2026 and November 6, 2026 respectively.
| Parameter | RPN Calc | Halcyon Calc |
|---|---|---|
| Price | $0.99 — better | $4.99 |
| Rating | 4.0 (6 ratings) | 4.9 (18 ratings) — better |
| Positive reviews | 34.3% of reviews | 100.0% of reviews — better |
| Number of ratings | 6 | 18 — better |
| Update frequency | Every 3 months — better | Every 4 months |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free — better | Paid |
| Devices | iPhone, iPad, Apple Watch — better | iPhone, iPad |
| Requires iOS | 16.0 — better | 16.6 |
| Further details — not scored | ||
| Size | 3 MB | 10 MB |
| Age rating | 4+ | 4+ |
| Developer | James Mattis | Halcyon Touch Software |
Customer experience
RPN Calc
Halcyon Calc
In-app purchases
RPN Calc
No in-app purchases
Halcyon Calc
No in-app purchases









