Measurement uncertainty
The range of possible values around a measured quantity within which the true value is likely to lie, arising from limitations of instruments, methods, and experimental conditions. Uncertainty is expressed as an absolute value (±) or as a percentage of the measurement. Every measurement has uncertainty; precision depends on the instrument's sensitivity.
Formula
Percentage uncertainty = (absolute uncertainty / measured value) × 100%
Real World
When Usain Bolt ran 9.58 s in Berlin 2009, the timing system had an uncertainty of ±0.001 s — small enough to confirm the record but still acknowledged in official IAAF documentation.
Exam Focus
For repeated readings, use half the range as the uncertainty — state whether errors are random or systematic for full marks.
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