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Percentage uncertainty

From a value and its uncertainty, from repeats or from a scale.

From a value and its uncertainty

From repeat readings (half the range)

From the scale of an instrument

The measurement needs

Worked example

Repeat readings 12.1, 12.3 and 12.5 s. Mean = 12.3. Uncertainty = half the range = (12.5 − 12.1) ÷ 2 = 0.2. Percentage uncertainty = 0.2 ÷ 12.3 × 100 = 1.6 %.

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