- The National Prototype of the Kilogram of Japan, which was the national mass standard through the five eras of Meiji, Taisho, Showa, Heisei, and Reiwa, is designated as an Important Cultural Property
- The National Prototype of the Kilogram of Japan is a weight made of platinum-iridium alloy, and it has been preserved by the wisdom and tireless efforts of our predecessors
- The National Prototype of the Kilogram of Japan has played an important role in the internationalization of the measurement unit system of Japan and has supported subsequent industrial development
National Prototype of the Kilogram of Japan, which was used as the national mass standard for about 130 years through the Meiji, Taisho, Showa, Heisei, and Reiwa eras
On October 15, 2021, the Council for Cultural Affairs submitted a report to the Minister of Education, Culture, Sports, Science and Technology (MEXT) proposing that the National Prototype of the Kilogram of Japan and related prototypes kept by the National Institute of Advanced Industrial Science and Technology (AIST) be given the status of Important Cultural Properties on the basis of the deliberations and decisions of the Subdivision on Cultural Properties of the Council for Cultural Affairs held on the same day.
For about 130 years from 1889 to 2019, the kilogram, the unit of mass, was defined as the mass of the International Prototype of the Kilogram. The National Prototype of the Kilogram of Japan kept by AIST is one of the copies of the International Prototype of the Kilogram. In 1891 (24th year of the Meiji era), the National Prototype of the Kilogram of Japan was set as the national mass standard, and a unit system in conformity with the international metric system was established from the conventional unit system, where the units of the shaku (approximate. 30.3 cm) and the kan (approximate. 3.75 kg) had been used.
The internationalized unit system played an important role as an intellectual infrastructure to introduce Western knowledge and technology when Japan was moving toward modernization. The National Prototype of the Kilogram of Japan continued to play a role as the national mass standard for about 130 years across the five eras of Meiji, Taisho, Showa, Heisei, and Reiwa until 2019 (1st year of the Reiwa era) and greatly contributed to the modernization and industrial development of Japan.
On the other hand, the National Prototype of the Meter of Japan was the national length standard for about 70 years until 1960 (35th year of the Showa era) and, it has already been designated as the Important Cultural Property “Prototypes related to the Meter Convention and the act for measurement units”. The definition of the kilogram was revised in 2019 and is now based on the Planck constant. In response to this redefinition, the historical and academic values of the National Prototype of the Kilogram of Japan and related prototypes were evaluated, and they are additionally designated to the Important Cultural Property “Prototypes related to the Meter Convention and the act for measurement units”.