In 1968, in the Metric Study Act (Pub. L. 90-472, August 9, 1968, 82 Stat. 693), Congress authorized a three-year study of systems of measurement in the U.S., with particular emphasis on the feasibility of adopting the SI.
In the International System of Units, the position of the moving object is measured in meters relative to the origin, while the time is measured in seconds.
This was the reason why in 1889 by the 1st General Conference on Weights and Measures (CGPM) of the Bureau International des Poids et Mesures (BIPM) the three characteristics length, mass, and time were selected and in 1954 during the 10th CGPM three more characteristics were added and it was decided to derive an International System of Units (SI) that should cover all physical characteristics.
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In 2013 the UK National Physical Laboratory used microwave and acoustic resonance measurements to determine the speed of sound of a monatomic gas in a triaxial ellipsoid chamber to determine a more accurate value for the constant as a part of the revision of the International System of Units.
In the International System of Units (SI), the only prototype remaining in current use is the International Prototype Kilogram, a solid platinum-iridium cylinder kept at the Bureau International des Poids et Mesures (International Bureau of Weights and Measures) in Sèvres France (a suburb of Paris) that by definition is the mass of exactly one kilogram.
The measurement of time is overseen by BIPM (Bureau International des Poids et Mesures), located in Sèvres, France, which ensures uniformity of measurements and their traceability to the International System of Units (SI) worldwide.