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The maintainer reads every message. Reports of wrong numbers or unclear explanations are the most useful, and a verified error is corrected and added to the public corrections log.
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What to include
For a wrong result, say which calculator, the values you entered and what you expected. A link to the page is enough to identify the calculator. There is no support desk and no guaranteed reply time.
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Educational tool — not a substitute for a licensed engineer or the official code text.