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Accuracy and precision defined

Short answer

Accuracy is closeness to the true value; precision is repeatability. Tightly grouped readings away from the true value are precise but not accurate. Systematic errors affect accuracy, random errors affect precision.

Describe the terms accuracy and precision used in surveying with examples.

Accuracy is the degree of closeness of a measured value to the true value. It shows how correct the result is.

Precision is the degree of closeness of repeated measurements of the same quantity to one another. It shows how consistent the measurements are, whether or not they are close to the true value.

Example

The true length of a line is 100.000 m.

ObserverReadings (m)MeanComment
A100.02, 99.98, 100.01, 99.99100.00Close to the true value and to each other: accurate and precise
B100.52, 100.51, 100.52, 100.53100.52Readings agree with one another but are far from the true value (e.g. tape too short): precise but not accurate
C99.5, 100.6, 100.1, 99.8100.0Mean is near the true value but the readings scatter: accurate on average, not precise

A target-shooting example: shots grouped tightly but away from the bull's eye are precise but inaccurate; shots grouped tightly around the bull's eye are both accurate and precise.

High precision does not guarantee accuracy, because a systematic error (like a wrong tape length) affects all readings equally. Accuracy needs both low systematic errors and high precision.

✓ Answer checked by Claude Opus 5.5 (high effort)

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