How the tools are checked

Automated tests before every change

Every calculation has automated tests, currently around 1,500. They check known answers, such as 100 °C being 212 °F and week 1 starting correctly at the turn of the year, but also edge cases and invalid input.

The tests run every time the site is built. If a single one fails, no new version is built, and the one already online stays in place.

The tests also cover things that are not arithmetic: that every page has its own address in every language, that reversed addresses lead to the right page, and that the colours in light and dark mode have the contrast needed for the text to be readable.

Independent recalculation

Results have been recalculated independently of the site’s own code, with other tools and formulas, for loans, compound interest, statistics, sunrise, week numbers and unit conversions among others.

Sources

Outside data comes from those responsible for it: exchange rates from the European Central Bank, consumer price indices from national statistics offices and the World Bank, VAT rates from each country’s tax authority, and sun times using NOAA’s method of calculation. The sources are linked under each tool.

Data that changes

VAT rates, public holidays and other rules change by decision. Once a week, what the site says is compared with official sources, both what applies today and what has already been decided for the future, and any difference is corrected.

Consumer price indices are fetched every month when the statistics offices publish new figures. Tools built on such data show when it was last updated and warn if it is older than expected.

Historical units

The historical units are based on legislation, archives, metrological reference works and academic studies, with the source given for each unit. Where sources disagree, both figures are shown rather than an average, and popular explanations without evidence are reported as exactly that.

Each language’s units have been checked in a separate review against sources other than those the entry already cited. An automated test also recalculates 171 relationships within the systems, for example that a yard is three feet, because an error in a copied figure almost always shows up as a broken relationship.

Everything is calculated in your browser

The calculations run in your browser, and what you type in is not sent to any server. That also means the tools work offline once the page has loaded. What does happen is described on the Privacy and cookies page.

If you find an error

Write to quaestio.application@gmail.com and describe which page it concerns, what you entered and what you expected. The error is corrected in every language at once, and a test is added so that the same error cannot come back.