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 common technique for tabulating nuclear mass is frequently utilized. The atomic nucleus's mass can be roughly estimated (with less than 0.1% error for most nuclides) by its mass number, implying that a significant portion of the nucleus's mass comes from protons and neutrons.