Metrology is the science of measurement and it is a vital part of everyday life. For example, food is bought by weight, water and electricity are metered, and instruments analyzing blood samples must be precise. It is easy to understand that faulty measurements by medical devices, or in the maintenance of critical components such as for vehicle brakes or aircraft engines, can be highly dangerous. Accurate measurements and measuring equipment are needed for the protection of health, safety, the environment and consumers. They are vital too in contracts between individual business partners and in world trade in general.
Balances and other instruments in laboratories need to be calibrated so that they can provide reliable measurements. Firms cannot satisfactorily implement process controls to manufacture a product to standardized characteristics if control instruments such those measuring pressure and temperature are not properly calibrated.
Confidence in national measurement is assured by a national metrology institute (NMI) when it becomes signatory to the Mutual Recognition Arrangement of the International Committee of Weights and Measures (CIPM MRA). The CIPM MRA provides the institutional and technical framework for NMIs to recognize each other’s measurement standards and calibration certificates, thus supporting world trade.

LEGAL METROLOGY
Concerns the regulatory requirements of measurements and measuring instruments for the protection of health, public safety, the environment, enabling taxation, protection of consumers and fair trade.
APPLIED OR INDUSTRIAL METROLOGY
Concerns the application of measurement science to manufacturing and other processes and their use in society; ensuring the suitability of measurement instruments, their calibration and quality control of measurements.
SCIENTIFIC OR FUNDAMENTAL METROLOGY
Concerns the establishment of measurement units, unit systems, the development of new measurement methods, realization of measurement standards and the transfer of traceability from these standards to users in society.