Progress Towards the Establishment of Various Redefinitions of SI Unit “Metre” at CSIR-National Physical Laboratory- India and its Realization

Length measurement has been an indispensable part of human life since the ancient era till present days. Length and area measurement got importance from very early Indus Valley civilization for construction of roads to measurement of agricultural land. In India, length measurements were defined in Indus Valley civilization and rulers had rules for length measurements. Mughal and British adopted the measurement system contemporary to the international system of units available and were used in the country. During twilight years of the regime of British government, plans for setting up an institute for measurement standards were made and a national institute of measurements was founded in 1942. Within the first decade of laying the constitution of India, SI units were adopted. In this paper, we describe the history and advancements in the progress towards length measurement through its various redefinitions from time to time. It covers the evolution of SI unit of length “Metre” through its diversified redefinitions from the ages of body parts to latest quantum standards.