Metrology, the science of measurement, is crucial for many sciences and technological developments. Since metrology helps to improve many other sciences, the book reflects in general metrology and some special metrological approaches at different fields such as radiation and frequency measurements in detail. This book also focuses on technical testing and control applications in the industry. It also intends the fundamentals of metrology concerning the related standards and systems of units. In addition, the book considers the calibration of measurement instruments and measurement uncertainties as the basic requirements of the related quality standards.