Measurement is the process of determining the magnitude of a physical quantity by comparing it to an accepted standard. Whether measuring the length of a steel bar, the mass of a component, the temperature of a furnace, or the voltage in an electrical circuit, measurement allows physical properties to be expressed using numbers and units.
The ability to measure accurately is fundamental to science, engineering, manufacturing, and commerce. Modern society depends on measurement systems that allow people in different locations to communicate quantitative information consistently. Without standardized measurement, it would be impossible to manufacture interchangeable parts, conduct scientific research, construct buildings, or trade goods fairly.
Every measurement consists of two parts: a numerical value and a unit. For example, a length may be reported as 25 millimeters, a mass as 5 kilograms, or a temperature as 100 degrees Celsius. The numerical value indicates how much of a quantity is present, while the unit provides a reference against which that quantity is compared.
Measurements are used to describe many physical quantities, including length, mass, time, temperature, electric current, force, pressure, and energy. The specific units used depend upon the measurement system being applied. Throughout history, many systems of measurement have been developed, including customary units based on human dimensions, national systems of standards, and the modern International System of Units (SI).
In engineering and manufacturing, measurement is often associated with the size of a part, such as its length, diameter, or thickness. However, measurements are used to verify many other characteristics as well. A component may need to be straight, flat, round, perpendicular to another surface, or located in a specific position relative to other features. Measurements help determine whether a part meets these requirements and can function as intended within an assembly. Engineering drawings communicate these requirements through dimensions and tolerances, while measurement provides the means to verify them.
The science of measurement is known as metrology. Metrology encompasses the development of measurement standards, the design and use of measuring instruments, calibration, traceability, and the analysis of measurement results. It provides the foundation for quality control, scientific research, and industrial manufacturing.
Modern measurement relies upon carefully maintained standards that allow measurements made in different laboratories, factories, and countries to be compared with confidence. National metrology institutes, such as the National Institute of Standards and Technology (NIST), help maintain these standards and provide traceability to internationally recognized references.
An understanding of measurement begins with an understanding of units and standards. From this foundation, more advanced topics such as systems of measurement, accuracy and precision, significant figures, measurement error, calibration, traceability, uncertainty, and industrial inspection can be explored.
