Japan's Meter, Kilogram Prototypes Shown to Press

   Tsukuba, Ibaraki Pref., May 13 (Jiji Press)--The National Institute of Advanced Industrial Science and Technology, or AIST, showed Japan's meter and kilogram prototypes to the press on Monday, ahead of the 150th anniversary later this month of the conclusion of the Meter Convention in 1875.
   Near the end of the 18th century, 1 meter was defined as one-10 millionth of the distance from the equator to the North Pole along a meridian through Paris and 1 kilogram as the mass of a liter of water.
   International meter and kilogram prototypes made of platinum-iridium alloy were created after the convention that standardized the units of measurement was concluded. Copies of them were delivered to Japan in 1890.
   With the advance of technologies making it impossible to ignore the metal prototype's deterioration over time as a margin of error, the meter standard was changed from the metal prototype to one employing the wavelength of light in 1960. A method using the distance light travels in a certain amount of time was adopted to define 1 meter in 1983.
   The kilogram standard was updated to one using the Planck constant, a minimum unit of light energy, in 2019.

(2025/05/13-22:14)