Accuracy and precision
In metrology:
Accuracy is a qualitative term that describes how close a set of measurements are to the actual (true) value.
Precision describes the spread of these measurements when repeated. A measurement that has high precision has good repeatability.
Making a good measurement is a bit like hitting a target, and the chances of a good result that makes sense are greatly increased if you make several attempts.
The difference between accuracy and precision is illustrated here. The bull’s-eye in the target represents the true value of a measurement.
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