It is one of the predominant methods for tabulating nuclear mass. The mass of an atomic nucleus is well approximated (less than 0.1% difference for most nuclides) by its mass number, which indicates that most of the mass of a nucleus arises from mass of its constituent protons and neutrons.
One primary method employed to determine nuclear mass is widely used. The atomic nucleus's mass can be approximately calculated (with less than 0.1% error for most nuclides) by its mass number, suggesting that a considerable portion of the nucleus's mass originates from protons and neutrons.