In modern mass measurement, weights are standard measuring tools for mass value transfer. The mass value is based on the platinum-iridium alloy kilogram prototype preserved in the French Bureau Internationale des Metrology as the only benchmark. All countries divide weights into national kilogram benchmarks, national kilogram secondary benchmarks, kilogram working benchmarks, and working benchmark groups composed of kilogram multiples and weights and various working standard weights.
There is only one national kilogram benchmark for each country. China's national kilogram benchmark is the platinum-iridium alloy kilogram benchmark weight numbered 60, which was verified by the International Bureau of Weights and Measures in 1965. The national kilogram standard, the national testimonial standard, the national secondary standard for the kilogram, the working standard for the kilogram, and the standard weights form a mass value transfer system. To measure various objects of different masses, the kilogram working benchmark is equipped with a set of working benchmark groups consisting of its multiples and weights, from large to small in mass, with the least number and capable of forming any value. The working reference group and standard weights are usually divided into the kilogram group (1-20kg), gram group (1-50g), and milligram group (1-500mg). The weight-increasing group was used on the platform scale). The combination of weights is usually 5, 3, 2, 1, 5, 2, 2, 1, and 5, 2, 1, 1.