Metrology

From Academic Kids

Metrology is the science and process of ensuring that a measurement meets specified degrees of both accuracy and precision.

Accuracy is the "correctness" of a measurement; that is, how closely it matches the value being measured. Precision, on the other hand, is how detailed a measurement is. By way of illustration, imagine that you have two Voltmeters, A and B, measuring a voltage source of 1.56678 volts. Voltmeter "A" can only display a reading of 1.56 volts; Voltmeter "B" can display a reading of 1.49992847 volts. Voltmeter "A" is ACCURATE (its measurement is more correct), but not precise; Voltmeter "B" is PRECISE (more detailed), but not accurate.

Metrology, then, is the process by which both accuracy and precision are tested and adjusted for (if necessary). This is accomplished through a hierarchical system where each measuring device is compared against an external reference, known as a Standard; each Standard is then tested against a higher-level (more accurage and precise) Standard, which is compared against an even HIGHER Standard, and so on. In the United States, the master reference Standards are maintained through the National Institute of Standards and Technology (http://www.nist.gov/), or NIST (formerly known as the National Bureau of Standards). By convention, a Standard is ten times more accurate and precise than the measurement device being tested.

The process of comparison against a Standard, and making any necessary adjustments, is commonly called Calibration. Detailed records are maintained for each item that is calibrated to ensure "traceability", and that the item met clearly identified specifications for both accuracy and precision in all its operating parameters.

Collaboration between NIST and its counterparts in other countries and with the International Bureau of Weights and Measures (BIPM) ensures the highest achievable Standards.

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