--- title: "Precision, accuracy and significant figures" description: "Distinguish precision, agreement between repeated readings, from accuracy, closeness to a true or accepted reference value. Round measurements to stated decimal places or significant figures, and choo" canonical: https://lightmysky.com/learn/science/precision-accuracy-and-significant-figures-mt_auJqTemMpI source: https://lightmysky.com/learn/science/precision-accuracy-and-significant-figures-mt_auJqTemMpI.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Precision, accuracy and significant figures Distinguish precision, agreement between repeated readings, from accuracy, closeness to a true or accepted reference value. Round measurements to stated decimal places or significant figures, and choose instruments using their capacity and scale divisions. Subject: Science · Area: Scientific Inquiry · Ages 11 to 12 Page: https://lightmysky.com/learn/science/precision-accuracy-and-significant-figures-mt_auJqTemMpI ## Ready when they can - Explains the distinction between precision and accuracy with examples - Rounds measurements to an appropriate number of significant figures - Selects and uses a measuring instrument with suitable capacity and scale divisions for the quantity being measured ## Lesson: Precision and accuracy: why repeats aren't everything You have compared repeat readings before. Precision describes how closely readings agree under the same conditions. A smaller spread means greater precision in the same task. Accuracy describes closeness to a true or accepted reference value. Compare each reading with that reference. One reading can be close to a reference, but you need repeats to judge their agreement. *(drawing: The accepted reference is 19.0 g. These readings agree closely at 20.0 g and 20.2 g, but all lie above the reference.)* Measure the same object under the same conditions when checking repeats. A mean can reduce the effect of random variation, but cannot remove an offset shared by every reading. Check the zero setting, equipment and method against a trusted reference. A shared offset does not identify its cause by itself. Keep unusual readings, investigate them and explain any later exclusion. Choose a tool that holds the required volume and shows suitably small scale divisions. Resolution is the smallest change its scale or display shows. Finer divisions can reduce reading uncertainty, but do not prove accuracy. Inspect the actual markings rather than judging by capacity. For water, place a cylinder upright on a level surface. Read the bottom of the curved water surface at eye level. **Example.** Report the detail your method supports. Nearest 0.1 cm means one decimal place, the tenths place. To round 16.27 cm, keep the tenths digit, 2, and inspect the next digit, 7. This lesson uses the rule: 5 or more rounds up; less than 5 leaves the kept digit unchanged. The result is 16.3 cm. Significant figures report a measurement's detail; its last digit may still be uncertain. Start counting at the first nonzero digit. Ignore zeros before it. Count zeros between nonzero digits and final zeros in a decimal measurement. For example, 0.0304 m has three significant figures: 3, 0 and 4. The measurement 4.500 cm has four. Writing extra digits does not improve accuracy. **Example.** To round to a stated number of significant figures, count from the first nonzero digit. Keep the required digits and inspect the next digit. Use this lesson's rounding rule: 5 or more rounds up; less than 5 leaves the last kept digit unchanged. For 27.84 g to three significant figures, keep 2, 7 and 8. The next digit is 4, so report 27.8 g. **Recap.** Compare repeats for precision and a reference for accuracy. Check the tool and method, choose suitable divisions, and report only supported detail. *This lesson, its questions and its flashcards were written for this dataset.* ## Practice 17 questions on this page, each with its working shown. ## Needs first - [Accurate Measurement](https://lightmysky.com/learn/science/accurate-measurement-mt_Psun-u_lPf) ## Opens up - [Tables, charts, and graphs](https://lightmysky.com/learn/science/tables-charts-and-graphs-mt_YHsUhi4Prc)