Introduction to measurement
What is measurement?
Measurement underpins science, technology and industry. It enables processes to be run efficiently, and innovative and competitive products to be made. It impacts strongly on the welfare of a modern society and touches almost every aspect of daily life.
A measurement tells us about a property of something. It might tell us how heavy an object is, or how hot, or how long it is. A measurement gives a number to that property, expressed in the appropriate unit.
The units of measurement are standardised. The International System of Units (SI) is used worldwide so that measurements can be consistent everywhere.
Measurements are only ever estimates. Every measurement is subject to some uncertainty. The uncertainty of a measurement expresses how good the estimate is.
A good measurement result is incomplete without a statement of uncertainty, it is also accompanied by a level of confidence such as 95%. This means if you made numerous measurements, you could predict that about 95% of measurements would be within the stated uncertainty;
e.g. 2 cm ± 0.1 cm (uncertainty) at a confidence level of 95%
The uncertainty of a measurement should suit the need; a school clock need not have atomic accuracy.
Measuring equipment should be calibrated by comparison against a suitable reference which itself has been calibrated. An unbroken chain of calibrations that links back to national standards such as those used at the National Physical Laboratory (NPL) is known as measurement traceability.
Good measurement practice can reduce uncertainty and so improve the quality of processes and products.
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