Sources
Sources Policy
When a calculator needs an external source, how sources are chosen and kept current, and why elementary formulas do not need one.
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Elementary mathematical identities
Some calculators implement stable elementary mathematics, such as percentage identities or geometric formulas. These methods do not become more reliable by attaching an unrelated external article, so the formula itself is versioned and tested as the primary computational source.
External factual dependencies
When a result depends on changing facts, regulations, product specifications, official tables or datasets, the calculator should identify authoritative sources appropriate to that dependency and check whether the evidence is still current enough for the calculation.
Source selection principles
- Prefer primary, official or standards-based sources when they directly own the relevant fact.
- Corroborate a fact with an independent source where practical.
- Do not cite a source that does not actually support the claim or variable it is attached to.
- Re-check a source when the underlying fact can change.
User-supplied values
Where the right value depends on a specific product — such as the coverage printed on a box of flooring — the calculator asks you for it instead of guessing from a generic table, and says so beside the result.