I can define a Convertible Unit System

(User Story, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Convertible Units
Summary: A system is something like "Metric", "Modern English", "Medieval English", "Arabic", etc. It is a collection of Convertible Units.
The main thing about a System is that you should be able to use a single System for displaying, and have all Units convert to that System automatically.