Percentage error
A measure of how large a measurement uncertainty is relative to the measured value, expressed as a percentage. Calculated as (uncertainty / measurement value) × 100%. It allows comparison of measurement precision across different scales and experiments. A smaller percentage error indicates greater precision.
Formula
Percentage error = (uncertainty / measured value) × 100%
Real World
When NASA's Mars Climate Orbiter was lost in 1999, a unit conversion error produced a percentage error large enough to send the spacecraft off course by hundreds of kilometres — illustrating how a small absolute error can be catastrophic when expressed as a percentage of the required precision.
Exam Focus
Always show both the uncertainty and the measured value before dividing — examiners award method marks for the substitution step.
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