Janus Calculator vs RPN
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Janus Calculator
This app offers a unique dual-calculator interface, supporting both standard and Reverse Polish Notation. It features programmable functions, extensive scientific and financial tools, and includes physical constants and an advanced option calculator.
- Dual calculator interface (Standard and RPN)
- Programmable functions
- Finance and scientific functions
- Physical constants
- Black-Scholes option calculator
- Implied value calculation
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Two-sided calculator. Side A uses Standard Notation, Side B uses Reverse Polish Notation. Both calculators are programmable, include various finance and scientific functions, and the values of 45 physical constants. Also includes a Black-Scholes option calculator, including calculation of implied values for each of the inputs.
RPN
This app is a detailed simulation of a 1973 scientific calculator, offering a photorealistic interface and all original functions. It includes powerful enhancements for modern use, such as complex number support and advanced date calculations.
- Photorealistic calculator simulation
- Full HP-45 function implementation
- Complex number support
- Advanced date and time functions
- Printer simulation for calculation records
- Stopwatch functionality
- Cut/copy/paste display values
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RPN-45 SD is a complete simulation of the scientific hand-held calculator HP-45 from 1973. Powerful enhancements turn the calculator into an amazingly useful tool for the 21st century. Features: • Photo-realistic look based on an existing device • Original LED display or high-contrast LCD display • Printer to keep a record of calculations • Animated keys with adjustable click sound and visual feedback • Simulation of the HP-45's computation times (may be disabled) • All functions and operations of the HP-45 fully implemented • "Secret" stopwatch implemented, extensible from 12 to 100 hours capacity • Stopwatch may be preset to current time • Swipe left across display to correct wrong number entries • Cut/copy/paste of display value • Tap display to show stack and all memory registers • Complex numbers may be used in almost all operations • Non-volatile stack and registers • 18 storage locations (9 in complex number mode) • Exponentiation and factorial accept any values (incl. complex) • Optional hyperbolic functions • Logarithm to any base (incl. complex) • Solve linear equations in two or three unknowns • Solve quadratic and cubic equations • Normal distribution, Pearson correlation coefficient of paired variables • Linear regression with estimates • Weighted mean • Permutation, Combination (binomial coefficient) • Integer and fractional part of a number • Display rounding • Random numbers in any range, integer or real • Day of the week of any date between Jan 1, 0001 and Dec 31, 9999 • Easter date for any year between 1583 and 4099 • Support for Julian dates • Date and day of the week a number of days away (past or future) • Number of days between any two dates • Last Stack operation • Show display value in hexadecimal • Percentage of sum • Register arithmetic includes summation registers and LAST x • Indicators for active prefix keys • Angular mode indicator • Localized decimal point • Thousand's separator • Clear all registers • Backup registers in a protected area Double-tap the display for some basic hints. Also available for iPad (RPN-45 HD). For more information, a manual and sample calculations visit the RPN-45 website: cuveesoft.ch/rpn45/en What users said: "Have been using HP RPN calculators since HP-35 first came out. The CuVée versions for Apple products are the best emulations by far. I have, and regularly use, them all." "This app is a great emulator of the classic HP-45 Scientific Calculator, in look, feel and function. It keeps getting better and better with each update." "This is the most like the real thing that I've used. I've bought others but keep coming back to this App. It's photorealistic, the LEDs appear the way the real ones do, and the buttons almost give the same satisfying feedback of the real thing."
Screenshots
Verdict
The clearest difference is price: Janus Calculator at Free against RPN's $1.99. RPN's advantage is rating (4.3 vs 2.0) and update cadence (every 4 months vs every 45 months). 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
Janus Calculator is free to download; RPN costs $1.99 up front. Neither carries in-app purchases, so what you see is what you pay.
RPN holds the better App Store score, 4.3 against 2.0. That said, the two scores are not equally well evidenced: RPN has 15 ratings behind it against 1, so its average is the more settled of the two. Written reviews complicate that: 83% of Janus Calculator's written reviews are positive against 82% of RPN's, so the app with the better star average is not the one people write more warmly about.
Janus Calculator ships an update every 45 months, RPN every 4 months. Both last shipped on November 1, 2026.
| Parameter | Janus Calculator | RPN |
|---|---|---|
| Price | Free — better | $1.99 |
| Rating | 2.0 (1 ratings) | 4.3 (15 ratings) — better |
| Positive reviews | 83.3% of reviews — better | 81.8% of reviews |
| Number of ratings | 1 | 15 — better |
| Update frequency | Every 45 months | Every 4 months — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free — better | Paid |
| Devices | iPhone, iPad, iPod — better | iPhone, iPod |
| Requires iOS | 26.2 | 12.0 — better |
| Further details — not scored | ||
| Size | 1 MB | 14 MB |
| Age rating | 4+ | 4+ |
| Developer | Geoffrey Domm | CuVee Software |
Customer experience
Janus Calculator
RPN
In-app purchases
Janus Calculator
No in-app purchases
RPN
No in-app purchases









