https://doi.org/10.1351/goldbook.U06554
Non-SI unit of mass (equal to the @[email protected]), defined as one twelfth of the mass of a carbon-12 atom in its @[email protected] and used to express masses of atomic particles, \(\text{u}\approx 1.660\ 5402(10)\times 10^{-27}\ \text{kg}\).
Sources:
Green Book, 2nd ed., p. 75 [Terms] [Book]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 997 [Terms] [Paper]