Abstract: In an embodiment, a method of creating a standard unit of value for non-uniform commodities, such as diamonds, is provided. The method comprises defining, for a particular diamond cut, a plurality of quality classes and a plurality of carat classes; for each combination of quality class and carat class, creating a list of all qualifying diamonds; normalising the value of the diamonds in the list of qualifying diamonds over a fixed period, sufficient to measure changes of value. This may include the steps of obtaining or determining the monetary value for each of the diamonds in the list, determining the average of all these values, and dividing each value in the list by the average so as to obtain an average relative value for each diamond in the list. The method concludes by selecting a group or parcel of diamonds that collectively, in the aggregate, define the standard unit of value.