Sources & References

How sources are ranked

1. Official and standards-body publications: for example NIST for units and measurement, the BIPM for the SI, the IRS and the Social Security Administration for United States tax and benefit figures, and GOV.UK for UK stamp duty.
2. Open textbooks: OpenStax titles in mathematics, statistics, physics, chemistry, accounting, economics and finance.
3. Original and primary works where a formula has a well-known origin, such as Shannon’s paper for the diversity index.
4. Standards and conventions from technical bodies such as ISO and the IETF.
5. Stated definitions: where no authoritative standard exists, such as many marketing and operations ratios, the page says so and states the definition it uses.

How sources are cited and checked

Each calculator lists its sources at the bottom of the page. Citations name the publication and publisher, and a year or edition where it matters. They show where the method comes from; they are not a claim that a particular chapter or page was re-read unless the page says so, and no web addresses or chapter numbers are invented. Figures that change by year, such as tax limits, are tied to the year shown and are compared with the issuing authority’s own publication, with the date of the check recorded.

No endorsement

Naming an organisation or publication as a source does not mean it has reviewed, approved or endorsed Calculator Atlas, and none has.

Standards that are not freely available

Where a calculator names a paid standard, for example from ASTM or ASCE, the relevant values are cited, not reproduced.

Found a problem with a source?

Tell us through the contact page or read the corrections policy. For how calculators are checked, see the methodology.