The constant Mass Flow principle is a system that adds a predetermined mass of oxygen to the loop. The method is based on a hole in a nozzle and a fixed intermediary pressure. Apart from a great number of external factors the quantity of oxygen added to the loop depends mainly on the nozzle length, hole diameter, and IP. So a pressure reducer with a fixed IP adds oxygen to a nozzle. This nozzle adds independent of depth a fixed amount of oxygen to the loop (the quantity of metabolized oxygen is not dependant of depth). Imagine the system adds 1 ltr of oxygen per minute. The process of oxygen metabolizing is depending on labour, condition, size of the diver, and other factors. Normally the usage is between 0.5 ltr at rest to max 3.0 ltr when swimming against the current with stress. In case the system does not supply enough oxygen the diver has to bypass the CMF system to increase the loop volume. In case the diver is at rest the CMF system adds to much oxygen, and the loops will purge the extra oxygen by means of a overpressure valve.