In physics and chemistry, the atomic mass constant, is one twelfth the mass of an unbound atom of carbon-12 at rest and in ground state. The atomic mass constant is used to define the atomic mass unit. This constant s a non-SA unit accepted for use with the SI. The atomic mass unit is obsolete and has been replaced by the term unified atomic mass unit (symbol: u, and also known as a dalton (symbol: Da) ) This constant returns the atomic mass constant energy equivalent in MeV/`c^2` (megaelectronvolts per speed of light squared)