# Measurement – or how we put numbers to things

This page provides a brief introduction to the important principles in measurement. It then gives an overview of key principles covered in more detailed pages. Measurement is of central importance to trade, science and engineering. It enables us to know how much of something we are buying, to know that things will fit together and to compare the results of experiments. It might at first seem quite simple. But measurement has occupied some of the greatest minds and been at the forefront on science throughout history!

## Dimensional Measurement

My particular focus is on dimensions: lengths, angles, straightness and flatness etc. The fundamental principles however, in particular uncertainty evaluation, can be applied to any form of measurement. You might want to read more about What Dimensional Measurement is and Why it Matters here.

• Length Measurement is perhaps what most people think of when they think of measurement. This page describes how length standards have developed over time. It also uses this history to explain the principles of traceability.
Laser Interferometers are the modern standard for accurate length measurement. They are allow us to replace a definition of the metre based on a physical metre bar held in Paris with a definition based on the speed of light. Interferometers have many uses in industrial and scientific measurement.
• Angle Measurement requires no reference standard, a circle can simply be sub-divided to obtain accurate angles. Combined with a relatively small length reference angular measurement can also be used to extended length measurement over large distances and to remote objects. It also provides practical ways of measuring 3D coordinates.
• Straightness and Flatness is important in the construction of machines and instruments as well as the use of conventional instruments.

## Metrology: The Science of Measurement

Metrology and involves principles such as uncertainty, traceability and confidence. When understood these principles allow us to prove, with known statistical confidence, whether or not something conforms to a specification.

An introduction to the evaluation of uncertainty is given in addition to a complete explanation of the calculation on an uncertainty budget.