Before looking more closely at the manner in which chemists draw a connection between mass and the amount of atoms, molecules or ions in a sample, it is instructive to look at the internationally agreed system of units adopted for scientific measurement.  These units and their manipulation are, unfortunately, areas all too frequently overlooked, ultimately causing students – and, let’s face it, more than a handful of instructors and educators – to lack confidence and conviction in quantitative aspects of the physical sciences, an unhealthy situation to put it mildly.  The following routines, therefore, are not least in order of importance when it comes to successful solution of numerical problems involving physical quantities.