Section 16(4) in The Standards of Weights and Measures (National Standards) Rules, 1988
(4);The National Physical Laboratory shall arrange, where necessary, to have the national prototype and national standards of physical measurements realised and established in accor-dance with the recommendations of the General Conference on Weights and Measures and to get them calibrated or intercompared with reference to the appropriate international standards of physical measurements, at periodical intervals of not more than ten years.
