Editing Relative atomic mass (section)

=== Historical usage ===

Older (pre-1961) historical relative scales based on the atomic mass unit (symbol: ''a.m.u.'' or ''amu'') used either the [[oxygen-16]] [[relative isotopic mass]] or else the oxygen relative atomic mass (i.e., atomic weight) for reference. See the article on the history of the modern [[unified atomic mass unit]] for the resolution of these problems.