+ """A converter has a canonical name and a category. The name defines
+ a unit of measurement in a category or class of measurements.
+ This framework will allow conversion between named units in the
+ same category. e.g. name may be "meter", "inch", "mile" and their
+ category may be "length".
+
+ The way that conversions work is that we convert the magnitude
+ first to a canonical unit and then (if needed) from the canonical
+ unit to the desired destination unit. e.g. if "meter" is the
+ canonical unit of measurement for the category "length", in order
+ to convert miles into inches we first convert miles into meters
+ and, from there, meters into inches. This is potentially
+ dangerous because it requires two floating point operations which
+ each have the potential to overflow, underflow, or introduce
+ floating point errors. Caveat emptor.
+ """