Calculator requirements
- A clearly stated purpose and audience.
- Validated inputs and understandable results.
- The formula or method used.
- A worked example with reproducible numbers.
- Rounding rules, assumptions and known limitations.
- Frequently asked questions that add genuine context.
Testing
Calculator logic should include deterministic test cases covering ordinary values, zero values, boundary values and overnight time handling where applicable.
Current-data policy
Tools depending on taxes, statutory rates or jurisdiction rules must display their effective date, identify primary sources and be reviewed when rules change. A calculator must be withdrawn or clearly marked when its data cannot be verified.
Corrections
Material formula or data corrections should be documented in the project release notes and deployed promptly.