Comparison

Twin Calculator vs O'der stack

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

Head to head
About

Twin Calculator

This app offers two independent calculators in a single interface, allowing for seamless transfer of results between them. It supports basic arithmetic, percentages, and parentheses, with a clean design that adapts to light and dark modes. Ideal for managing multiple calculations simultaneously.

Highlights
  • Two independent calculators
  • Transfer results between calculators
  • Supports parentheses and percentages
  • Displays formulas and results
  • Adapts to light/dark mode
  • High precision calculations
Features
Read full description

Two Calculators. One App. Twin Calculator is a versatile calculator app that lets you use two independent calculators in one convenient place. With MAIN and SUB, you can perform separate calculations and transfer results from one calculator to the other without entering the numbers again. ■ Two Calculators, One Convenient Experience MAIN is blue. SUB is green. On iPhone, simply swipe across the display area to switch between the two calculators. On iPad, use both calculators side by side in portrait or landscape orientation. ■ Transfer Results Between Calculators Send a result from MAIN to SUB, or from SUB to MAIN. Easily reuse calculation results without memorizing or retyping numbers. Perfect for working with multiple calculations. ■ Useful Calculation Features • Addition, subtraction, multiplication, and division • Calculations with parentheses • Percentage calculations • Store and recall α and β constants • Display both formulas and results • Calculations involving decimals and negative numbers ■ A Fresh, Easy-to-Use Design Enjoy rounded buttons, spacious formula displays, and a clean interface designed for everyday use. The app automatically adapts to your device's Light or Dark Mode setting. ■ Improved Calculation Precision Intermediate calculations retain higher precision, while results are displayed with up to 10 decimal places. Calculation values are kept separate from formatted display text, helping maintain precision during continuous calculations and transfers. Whether you're shopping, managing your budget, working, or studying, Twin Calculator makes everyday calculations more convenient. Discover the flexibility of having two calculators in one app. REO Factory

About

O'der stack

Features
Read full description

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

Twin Calculator4 screens
O'der stack4 screens

Verdict

The call

The clearest difference is in-app purchases: Twin Calculator at none against O'der stack's 3. O'der stack's advantage is ads (none vs shown) and update cadence (every 3 months vs every 7 months). On price, 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

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. O'der stack sells 3 one-off in-app purchases. Twin Calculator asks for nothing beyond the download.

UpkeepUpdate frequency

Twin Calculator ships an update every 7 months, O'der stack every 3 months. The most recent releases landed on November 6, 2026 and October 25, 2026 respectively.

Scorecard3 real differences · 7 level
Twin Calculator versus O'der stack: the parameters behind the verdict, then further details
ParameterTwin CalculatorO'der stack
PriceFreeFree
Rating3.0 (2 ratings) — better—
Positive reviews0.0% of reviews—
Number of ratings2 — better—
Update frequencyEvery 7 monthsEvery 3 months — better
AdsYesNo — better
In-app purchasesNo — betterYes
MonetizationAd-supported—
DevicesiPhone, iPad, iPodiPhone, iPad, iPod
Requires iOS15.0 — better15.6
Further details — not scored
Size8 MB59 MB
Age rating4+4+
DeveloperR.E.O. FactoryICT Fractal Inc.

In-app purchases

None

Twin Calculator

No in-app purchases

3 purchases

O'der stack

One-time3
  • Free trial for 7 days.Free
  • Activate for 1 month.$0.99
  • Activate for year.$9.99

Questions

Is Twin Calculator free?
Twin Calculator is free to download, with no in-app purchases.
Is O'der stack free?
O'der stack is free to download, with in-app purchases available.
Do Twin Calculator or O'der stack have ads?
Twin Calculator shows ads; O'der stack does not.
Which is updated more often, Twin Calculator or O'der stack?
Twin Calculator ships an update every 7 months, and O'der stack every 3 months. Most recently, Twin Calculator was updated on November 6, 2026 and O'der stack on October 25, 2026.

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