Stock is bought in one unit, held in another, and sold in a third more often than not: feed arrives by the tonne, is stocked in kilograms, and sells by the bag. Units of measure are the named measures themselves — each with the dimension it measures — and conversions are the defined bridges between them: one tonne is a thousand kilograms; one bag is twenty-five.
Two disciplines follow. First, every quantity names its unit, everywhere — on documents, in enquiries, in reports, in this module above all. It is a standing law of the application, not a formatting preference: a quantity without its unit is not a smaller piece of information, it is a different and dangerous one, and any screen that shows you a bare number has a defect.
Second, conversions are defined once, centrally, on the units themselves — never typed per document. A document may buy in tonnes because the conversion to the stocking kilogram exists; where no conversion exists between two units, that expression of the quantity is simply unavailable, never guessed at. Prices obey the same bridges (§6.7): a price set per tonne is expressed per bag on a document that sells bags, by the conversion — which is why a wrong conversion is never a display issue. It is a pricing and a stocking fact, and it is set up once, carefully (the Implementation Manual carries the steps), then left alone.