Checkable, dated, public
Calculator accuracy benchmark
Last updated: September 21, 2026. This page is the public record of how we verify calculator formulas - and what we found wrong and fixed.
The test suite
Every formula on this site is covered by an automated regression suite: 696 passing checks, 174 skipped, 2 known failures tracked publicly (psi-to-bar, growing-degree-days). Every site build runs the formula suite before deploy; a failing formula blocks the release.
Verified worked examples
Each example below was checked against the calculator's own formula code, not copy-pasted from a textbook.
| Input | Verified result |
|---|---|
| Rounding: 27.4567 to 2 decimal places | 27.46 (ties round half away from zero in edge cases - stated on page) |
| Significant figures: 12345 to 3 s.f. | 12300 |
| Fraction to decimal: 3/8 | 0.375 - terminating |
| Decimal to fraction: 0.375 | 3/8 (375/1000 reduced by GCD 125) |
Corrections log
We publish what we got wrong. Bugs found by the test suite are fixed, dated, and listed here.
- 2026-09-21 - Fraction to Decimal Calculator: 1/8 (0.125) was labeled 'repeating decimal, truncated' - false positive: 0.125 terminates. Fix: Repeating-note rule rewritten: a fraction repeats only when the reduced denominator has a prime factor other than 2 or 5. Regression test added.
Why this matters
Most calculator sites publish a formula once and never test it again. A wrong rounding rule or a mislabeled decimal is invisible to a human reader but changes real decisions. Our suite runs on every build, blocks deploys on failure, and every correction is public. If you find an error, it lands here with a date.