You can assign various units of measure for a generic article, and a subset of those units of measure for each variant. This allows you to buy and sell variants of the same generic article by different units of measure.

Suppose you have a generic article T-Shirt, which comes in S, M, L, and XL, and in white, black, red, and blue. You buy T-shirts in pallet loads and cartons. You sell all the shirts individually to your consumers, but in addition you sell the white shirt in bulk (cartons) to your wholesale customers for silk screening.

So although you can buy an assortment of T-shirts by the carton, you can only sell the black, blue, and red ones individually, while white shirts can be sold either individually or by the carton.