RPN Calc vs iCrucible
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.
iCrucible
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iCrucible is an AI tool for Materials Science. Using this app, you can learn about how AI tools work for materials screening, and may discover candidate compounds. Learn more at our website: https://www.rimcs.co.jp/ iCrucible makes a prediction of a ternary system on your iPhone or iPad without external services, using graph neural networks and crystal prototype databases bundled in the app. You can watch the phase diagram redrawn at the end of each stage during performing the prediction task. Note that it is the phase diagram at absolute zero (i.e., 0 kelvin) and around zero pressure (i.e., 0 kilobar). Performance It takes a few seconds to minutes depending on the creation settings and your device. The app has a multithreading option to accelerate the core of the AI tool - for example, computationally intensive tasks are sped up around 2.5x on M1 iPad Air. Chemical System A chemical system is selected by choosing three unique chemical elements from: • Element List (with group and period restriction) or • Periodic Table Materials Screening The materials screening is conducted by thresholding two values: • Predicative Variance • Stability (Energy above Convex Hull) Phase Diagram Drawing The drawing is customizable and responsive with useful features: • Formula Labeling • Stability Thresholding • Zoom • Mark Size • Font Size • Balloon with each compound information Confidence Chart The chart shows the distribution of predicative confidences, and provides an overall confidence of the system prediction and the phase diagram. Compound Table The table shows stable and metastable compounds with stabilities and predicative confidences, from which you can easily choose candidate compounds. Settings You can set the default preferences of the chemical system creation and the phase diagram drawing in the App's Settings. The entrance of the In-App Shop is also located in the App's Settings. We offer Free, Standard, and Premium plan. You can subscribe to one of Standard and Premium plan at the In-App Shop. The Shop's Help describes the system tiers used for the content management. Free features: • Free Elements: H to Ar. (*) • Ensemble Size: M = 1. • Prototype Database: Small only. • You can take a note about each chemical system to not forget any novel findings and great ideas. Standard features: • Standard Elements: K to Xe. (*) • Ensemble Size: M is not more than 5. • Prototype Database: Small, Medium, and Large. • You can sort chemical systems into Stocks that are a storage for them. • Chemical systems can be shared between your devices by peer-to-peer Wi-Fi networking. Premium features: • Premium Elements: Cs to Pu except Po to Ra. (*) • Ensemble Size: M is not more than 10. • Prototype Database: all scales, that is, Small, Medium, Large, and Huge. • Multithreading can be used to accelerate the core of the AI tool - for example, computationally intensive tasks are sped up around 2.5x on M1 iPad Air. * Noble gas elements are not available. Flame Gems You need flame gems for a non-free system creation, and can buy them at the In-App Shop. The Shop's Help describes how to consume flame gems and has the cost calculator. You have to buy no flame gems if you are on the Free plan. Terms of Use: http://www.apple.com/legal/itunes/appstore/dev/stdeula
Screenshots
Verdict
The clearest difference is price: iCrucible at Free against RPN Calc's $0.99. RPN Calc's advantage is in-app purchases (none vs 8). On update cadence, ads, device support and iOS requirement 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
iCrucible is free to download; RPN Calc costs $0.99 up front. iCrucible sells 8 in-app purchases, starting at $2.99 per month. RPN Calc asks for nothing beyond the download.
RPN Calc ships an update every 3 months, iCrucible every 5 months. The most recent releases landed on October 24, 2026 and October 27, 2026 respectively.
| Parameter | RPN Calc | iCrucible |
|---|---|---|
| Price | $0.99 | Free — better |
| Rating | 4.0 (6 ratings) — better | — |
| Positive reviews | 37.9% of reviews | — |
| Number of ratings | 6 — better | — |
| Update frequency | Every 3 months — better | Every 5 months |
| Ads | No | No |
| In-app purchases | No — better | Yes |
| Monetization | Free | — |
| Devices | iPhone, iPad, Apple Watch — better | iPhone, iPad |
| Requires iOS | 16.0 — better | 17.2 |
| Further details — not scored | ||
| Size | 3 MB | 172 MB |
| Age rating | +4 | 4+ |
| Developer | James Mattis | RIMCS LLC |
In-app purchases
RPN Calc
No in-app purchases
iCrucible
- Standard$2.991 Month
- Premium3 Days trial$4.991 Month
- Standard$29.991 Year
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- Premium$49.991 Year
- 500 Flame Gems$4.99
- 2,500 Flame Gems$23.99
- 5,000 Flame Gems$46.99
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- 10,000 Flame Gems$91.90









