Editorial standards
How Calculator24 builds and checks a calculator.
1. Start with the decision
Each page begins with a real task: estimate a monthly payment, convert a measurement, check a formula, or plan materials. We choose inputs and outputs that answer that task directly. Pages are consolidated when separate URLs would produce the same answer and explanation.
2. Use a traceable formula
The page states the equation and its assumptions in plain English. When a government agency, standards body, university text, or peer-reviewed publication defines the method, the page links to that source. If several accepted methods exist, the calculator identifies the selected method instead of presenting it as the only possible one.
3. Apply US conventions consistently
The primary locale is en-US. Numbers use commas for thousands and periods for decimals. Money defaults to US dollars where a calculator is specifically about the United States. US customary inputs such as inches, feet, pounds, miles, US gallons, and degrees Fahrenheit appear first where Americans commonly use them. Metric and international units remain available when they improve accuracy or comparison.
US customary conversions use published NIST factors. Tax, retirement, health, weather, and consumer pages identify the applicable agency and date because rules and thresholds can change.
4. Test behavior, not just examples
Automated checks cover known answers, both unit systems, invalid values, empty fields, and arithmetic limits. Browser tests cover live recalculation, keyboard use, sharing and export controls, and layouts down to 320 CSS pixels. Large results switch to compact or scientific notation so the page stays usable.
5. Explain limits beside the answer
A calculator can model the inputs it receives; it cannot inspect a contract, diagnose a condition, approve construction, or know a user's full circumstances. Each page names material exclusions and directs users to official documents or qualified professionals when the decision requires them.
6. Review and corrections
Detailed guides show an editorial review statement and update date. A material formula, threshold, unit, or source change requires a new review. Correction reports should include the page URL, inputs, observed result, expected result, and a supporting source. Verified errors are fixed in source, tested, and redeployed.
Source hierarchy
- US government agencies and standards bodies for current US rules and measurement standards.
- Original research, professional standards, and primary institutional guidance.
- University-level references for established mathematics and science.
- Secondary explanations only when a primary source does not address the practical question.
Platform standards
- NIST conversion guidance for US customary and metric relationships.
- W3C Web Content Accessibility Guidelines 2.2 as the accessibility benchmark.
- Google Search guidance on helpful, reliable, people-first content for discoverable editorial pages.