Since Air is defined by the CGA as containing 19% to 23.5% oxygen, describing nitrogen-oxygen gas mixtures up to 23.5% as Nitrox is just an obscure way of describing ordinary Air. Gas mixtures greater than 23.5% oxygen are what most people assume to be Nitrox, and of course there is also pure Oxygen. To avoid conflict with various dive supplier labeling and any misunderstanding about exactly what constitutes Nitrox, Dive Gear Express sometimes uses the phrase "suitable for service with compressed gases containing greater than 23.5% oxygen" to describe products that are both oxygen compatible and oxygen clean prior to initial use, especially in reference to cylinders and valves.