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The National Physical Laboratory (NPL) develops and maintains the UK’s primary measurement standards, which are used to check the accuracy of instruments used by thousands of other organisations making millions of measurements.
Did you know?
Accuracy is a qualitative term that describes how close the measurements are to the actual (true) value.
Precision describes the spread of these measurements when they are repeated.
Resolution is the smallest difference that can be meaningfully distinguished. For example, a change of one in the last place of a digital display.
Even when we are precise and accurate, there will still be some uncertainty in our measurements. The challenge for anyone doing measurements – and that is everyone (not just scientists and engineers) – is to assess the uncertainty and make it as small as appropriate for a particular application. For example, you do not need to measure cake ingredients with an uncertainty of millionths of a gram.
The difference between ACCURACY & PRECISIONWe use several words when describing measurement results.This poster should help you understand some of these words.
Missed the target centre, and the three attempts were not near each other.
Low accuracy and low precision
Three attempts were near the target centre, but were not near each other.
High accuracy, but low precision
Missed the target centre, but the three attempts were near each other.
Low accuracy, but high precision
Hit the target centre three times!
High accuracy and high precision
Incr
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Increasing precision
