Product specifications are statements, often quantitative, about a product. They can describe the amount of product provided (e. g. net weight of package contents), the concentration of a given ingredient or constituent (fat grams per serving), a measure of performance (output in lumens of a compact fluorescent light). Some specifications are qualitative rather than quantitative, but nevertheless lend themselves to rank ordering of preferences. An example would be presence of a feature being preferable over its absence (e. g. certified organic), or vice versa (loyalty card required to obtain at advertised price).