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Accuracy and Precision

Accuracy states how close the measurements are, on average, to the true value, i.e. how small the systematic error is. Precision states how tightly the measurements are clustered together, i.e. how small the spread (noise) is. A sensor can be precise without being accurate, and vice versa – the two properties are independent of each other.

xˉ=1n∑xi\bar{x}=\dfrac{1}{n}\sum x_iaverage of n measurements
s=1n−1∑(xi−xˉ)2s=\sqrt{\dfrac{1}{n-1}\sum(x_i-\bar x)^2}standard deviation (states precision, spread)

Symbols

xˉ\bar xaverage of the measurements
ssstandard deviation (spread)
xix_iindividual measurement

Example

Five measurements clustered tightly around 10.0 (true value 10.0):

Average ≈10.0\approx10.0 (accurate) and little spread (precise).

Precise is not the same as accurate – a scale can give the same (wrong) result every time.
Practise measurement for free →

← Serial Communication · Sampling and Nyquist →

Part of Embedded Systems and Instrumentation: Measurement.