RPN vs O'der stack
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
RPN
This app provides a photo-realistic simulation of a rare 1974 financial calculator, offering full functionality for loan amortization, saving plans, and depreciation. It features an authentic design with animated keys and an optional live register view.
- Photo-realistic design
- Live register view
- Animated keys with sound
- Full HP-70 function implementation
- Cut/copy/paste display value
- Built-in manual with examples
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RPN-70 HD is a complete, photo-realistic simulation of the financial hand-held calculator HP-70 from 1974. It handles loan amortization, saving plans, depreciation, and much more with ease. What users said: "Hard to find a decent calculator on iPad, try this one." "I don't normally write reviews but RPN-70 is just too fantastic to not get excited about. Apple should list this app under their Education category in the App Store and make it a must have for every college bound student. It is the best HP emulator in the market." "An incredibly well-engineered calculator app, and free, to boot!" "This is a really cool Financial calculator. Just like using the original HP-70. Accurate to the penny." Features: • Photo-realistic look based on an existing device • "Live" register view in landscape mode • Animated keys with click sound (adjustable volume) • All functions and operations of the HP-70 fully implemented • Simulation of the HP-70's computation time (optional) • Correct wrong number entries by swiping left across the display • Cut/copy/paste of display value • Visual indicators keep track of stored input parameters (optional) • Stack shown right below display (optional) • 10 non-volatile memory registers (optional) • Built-in short manual with many examples The HP-70 was discontinued after just one year. It is one of the rarest calculators, hard to find in any condition. NOTE: RPN-70 HD is a faithful simulation of a vintage HP-70 calculator, as has been verified against a real device using the examples in the Applications Cookbook section of the HP-70 manual. In certain cases, what may appear like a bug of the app is actually an idiosyncrasy of the HP-70. IMPORTANT: The HP-70 requires exactly three input parameters from the top-row keys, at least one of them being either "n" or "i". In other words, you can't use PMT, PV, and FV as input parameters simultaneously. A version for the iPhone named "RPN-70 SD" is also available. Visit the website: www.cuveesoft.ch
O'der stack
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O'der stack is a scientific calculator that is precise for up to 38 digits and is highly flexible. It can be used for various purposes, from learning to professional use, and has many functions that are convenient when mastered. The formulas described can be saved together with the results of the calculations and easily shared among members. Also, labels and memos can be set for formulas as well as each item that makes up the formulas. For example, by adding the label "radius" to "50" in 2 x 50 x π, it is possible to make the meaning of the formula even clearer. It is also perfect for entering explanations of formulas as memos and using them as tools to assist in learning. O'der stack offers two plans, the Pro plan which offers unlimited use of all functions, as well as the Free plan which makes it usable as an easy-to-use scientific calculator. —Functions— 1. A powerful editing function that allows partial overwriting of values without erasing the formula 2. Label and memo functions to support the understanding of formulas 3. A clipboard function that allows formulas to be pasted in notebooks, etc. 4. Setting the precision of calculations from 0 digits to 38 digits 5. Setting units (degrees/radians) for trigonometric functions 6. Setting the format of displaying results of calculations (normal notation, scientific notation, and percentage notation) 7. Basic functions (exponentiation and nth root) 8. Undo function —Pro plan— Please download O'der stack and try out the Pro plan for free for seven days. In addition to all the functions in the Free plan, the Pro plan allows for the activation of even more convenient functions. 1. Functions to save and load formulas and calculation histories 2. Function to share formulas and calculation histories 3. A sub-formula function that allows for the breakdown into several formulas and simple entry 4. 18 types of versatile and widely-used functions 5. 652 highly precise numerical and physical constants and observed values 6. Setting the format of displaying results of calculations (binary, octal, hexadecimal) - Each item can be selected from 8bit, 16bit, 24bit, 32bit, 64bit and 128bit. - Supports negative values and decimal points. - Negative values are displayed in complement. After the free trial has ended, if you would like to continue to use the Pro plan, a purchase of a non-autorenew-subscriptionis required. For a subscription, you can choose either a monthly purchase or yearly purchase, and the yearly purchase allows you to enjoy a discount worth two months of monthly purchases. Payment will be charged to your Apple ID account at the confirmation of purchase. If you purchase a plan during the effective period, it will be extended by the number of days of the purchased plan from the end date. The plan is effective on all devices linked to the purchased Apple ID account. Privacy policy https://ictfractal.github.io/official/PrivacyPolicy.html Terms of service https://ictfractal.github.io/official/AppTerms.pdf Disclaimer ICT Fractal Inc. does not guarantee the accuracy, credibility, and compatibility of the results of calculations and information provided through this app. Furthermore, it does not bear the responsibility for direct or indirect damages that might occur through this app.
Screenshots
Verdict
The clearest difference is in-app purchases: RPN at none against O'der stack's 3. RPN also leads on iOS requirement (12.0 vs 15.6). O'der stack's advantage is update cadence (every 3 months vs every 9 months) and device support (3 vs 1). On price and ads 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
Both are free to download. O'der stack sells 3 one-off in-app purchases. RPN asks for nothing beyond the download.
RPN ships an update every 9 months, O'der stack every 3 months. The most recent releases landed on June 1, 2026 and September 13, 2026 respectively.
| Parameter | RPN | O'der stack |
|---|---|---|
| Price | Free | Free |
| Rating | 5.0 (3 ratings) — better | — |
| Positive reviews | 86.7% of reviews | — |
| Number of ratings | 3 — better | — |
| Update frequency | Every 9 months | Every 3 months — better |
| Ads | No | No |
| In-app purchases | No — better | Yes |
| Monetization | Free | — |
| Devices | iPad | iPhone, iPad, iPod — better |
| Requires iOS | 12.0 — better | 15.6 |
| Further details — not scored | ||
| Size | 14 MB | 59 MB |
| Age rating | 4+ | 4+ |
| Developer | Willy Kunz | ICT Fractal Inc. |
In-app purchases
RPN
No in-app purchases
O'der stack
- Free trial for 7 days.Free
- Activate for 1 month.$0.99
- Activate for year.$9.99









