Unit groups are compilations of the different measurements that your products are available in. Unit groups include a base unit The initial measurement of a product. A unit group contains the lowest unit of measurement in which a product is available, such as a liter. It then lists all the different increments that this base unit is packaged in for sale, and indicates which one is the primary unit. and at least one primary unit The measurement used to define the most commonly sold unit of a product..