Fundamental Units and Constants in Metrology

Metrology includes precision, repeatability, and accuracy, which refers to how accurate the measured value is. It establishes a well-known understanding of the measuring process and the related units that are critical in connecting various human activities and ensures that these measurements are linked to reference standards, which are commonly referred to as traceability. This chapter introduces the fundamental units and constants in metrology through conversions between units and systems. Seven base units of the international system (SI) are known to be the second, meter, kilogram, ampere, kelvin, mole, and candela. A derived SI unit is a measurement unit that is devised for a derived quantity different from primary units. The international vocabulary of metrology defines traceability as the property of the result of a measurement or the value of a standard that can be related to stated references, usually national or international standards, by an unbroken chain of comparisons, all with stated uncertainties.