Too many digits can distract from a useful difference and imply more certainty than the information supports. Too few can hide the change the reader is trying to understand.
Choose a display rule that fits the quantity and the purpose. Keep the underlying values available where exact detail matters, and explain any formatting that turns a value into a range or an abbreviated label.
Check totals and small values after rounding. Displayed parts may not add exactly to a displayed total, and a small positive value may appear as zero. A brief note can resolve that confusion without filling the page with unnecessary decimals.
A small working example.
Consider showing an estimated duration to the nearest useful minute. Extra decimal places may suggest precision the underlying observation cannot support.
A note to keep beside it.
Show a reader how to question the result. A date, an explanation of coverage, or a visible range can make a chart more useful than extra precision.
- Match precision to the reader’s task.
- Keep exact values available when needed.
- Check the effect on totals and small values.
Follow a related question
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Related background to continue exploring this subject.
NIST: statistical engineering W3C: accessibility, usability, and inclusion