I should be able to specify a Unit Property

(User Story, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Properties
Summary: This has become High Priority due to the introduction of Duration. This is a classic metric: you're combining a quantity and a unit. Rather than doing this entirely ad-hoc, we should at least begin to introduce the key concepts behind Units, Conversions, and Metrics.