If an article contains a factual error, we correct the article and add a note at the bottom that describes what changed and when. We do not quietly change facts.
If a calculator produces a wrong result, we fix it and add a note to that tool's page describing the change and the date.
Minor fixes that do not change meaning, such as spelling or formatting, may be made without a note.
If a figure in an article was accurate when published but the underlying data has since been revised by its source, we may add an update rather than a correction.