Unit of Measure Primary vs Secondary

Summary:

We are trying to decide the most appropriate Unit of Measure to use in the Primary and Secondary fields. Example case; We have products that are sold in Sq Ft on a customer invoice and prices to the customer at the sq ft but the product is actually held in inventory in boxes, each box equals a specific amount of sq ft in the box, for example 1 box equals 15.54 sq ft (every SKU could have a different box to sq ft conversion). These same SKUs could be sold through our international subsidiaries in sq meters and/or box. These