R.A.M. AND R.M.M.

R.A.M. 是 relative atomic mass 的簡寫，中文是「相對原子質量」。
The relative atomic mass of an element is the weighted average of the relative masses (with the scale that the relative mass of ¹²C is defined as exactly 12) of all isotopes of the element.
某元素的相對原子質量，等於該元素的所有同位素的相對質量（根據以 ¹²C 的相對質量定義為準確 12 的標度）的加權平均數。

R.M.M. 是 relative molecular mass 的簡寫，中文是「相對分子質量」。
The relative molecular mass of a molecular compound is the sum of relative atomic masses of all atoms contains in the molecule.
某分子化合物的相對分子質量，等如該分子所含的原子的相對原子質量的總和。