Metrology is the scientific study of measurement that establishes a common understanding of units, which is crucial in linking human activities. The three overlapping activities of metrology are the definition, realization and traceability of the units of measurement. There are three basic sub-fields of metrology in which these activities are used. They are scientific or fundamental metrology, technical or industrial metrology, and legal metrology. Study of scientific metrology is focused on the units of measurement, the development of new measurement methods, the realisation of measurement standards, and the transfer of traceability from these standards to users in a society. Technical metrology studies are based on the application of measurement to manufacturing and other processes and their use in society. Legal metrology is based on the activities that result from statuatory requirements, measurements, units of measurement, measuring instruments and their methods of measurement. This book provides significant information of this discipline to help develop a good understanding of metrology and related fields. Its objective is to give a general view of the different areas of this discipline, and its applications. Researchers and students in this field will be assisted by this book.