How is the SI unit of mass defined and maintained?

The SI unit of mass, the kilogram, was originally defined as the mass of a specific platinum-iridium alloy cylinder kept at the International Bureau of Weights and Measures (BIPM) in France. However, this definition has changed. As of May 20, 2019, the kilogram is now defined by the Planck constant, a fundamental constant of nature. The new definition is based on precise measurements using a Kibble balance, which relates mass to electrical measurements. This method provides a more stable and accurate standard for the kilogram. In the NCERT syllabus, it is highlighted that these changes were made to improve the precision and reliability of scientific measurements.