The atomic mass unit

The evolution and realization of the atomic mass unit is reviewed. Prospects of replacing the prototype kilogram by an atomic mass standard are discussed. The problem is not one of finding an atomic mass unit, but rather in making the conversion from an atomic scale to the macroscopic world with adequate accuracy, so that the prototype kilogram may be replaced. The kilogram is of a convenient size for everyday use in commerce and technology and is roughly central between the masses of atomic particles and the mass of the universe. It is suggested that it is likely that scientists would wish to retain the present size for the basic mass unit, even if the definition were to be changed in favor of one based on some type of atomic quantity