Methodology

Choosing sources

Engineering facts are taken in this order of preference:

1. Standards bodies and national measurement institutes.
2. Manufacturer technical documentation and datasheets.
3. Universities and recognised engineering institutions.
4. Textbooks and primary literature.
5. Reputable secondary engineering references.

Competing calculators are useful for understanding what people are trying to do. They are not treated as a technical authority, and no text, table or example is copied from them.

Validating formulas

Each formula is written as a pure function, checked against a worked example from a source where one exists, and covered by unit tests including zero, negative, empty and out-of-range inputs. Worked examples printed on a page are produced by the same function that powers the calculator.

Units

Values are normalised to a single internal set of units — volts, amps, watts, watt-hours, amp-hours, ohms and hours — as soon as they are entered. Conversions happen at the boundary, never in the middle of a calculation.

Rounding and precision

Intermediate values are never rounded. Rounding happens once, at display time, and each result declares its own precision. Where a result is inherently uncertain, such as a runtime estimate, it is labelled as an estimate rather than presented to false precision.

Assumptions

Every model makes assumptions, and hiding them is what makes a calculator misleading. Each page lists what its model assumes and what it does not cover. Typical values loaded as defaults — depths of discharge, Peukert exponents, efficiencies — are described as typical published figures and can always be overridden.

Testing

• Unit tests for every calculation function and its edge cases.
• Component tests for labels, validation messages, unit switching and result updates.
• End-to-end tests against the production build, not just the development server.
• Automated accessibility checks, plus manual keyboard and screen reader review.
• Build-time audits for canonical URLs, metadata, structured data and internal links.

Updates

The "last meaningful update" date on a calculator changes only when the model, the sources or the guidance change. Rebuilding the site does not touch it, and no automated process refreshes dates to make pages look current.

Safety review

Tools that touch installation decisions — conductor sizing, protective devices, service loads — carry an explicit statement of the standard and jurisdiction they model, and say plainly that they are not a substitute for the wiring rules that apply where you are. Where a model cannot be verified against an authoritative source, it is not published.

Corrections

Errors in the mathematics are the highest priority fix on this site. If you find one, tell us and it will be corrected and noted.