Gauges monitoring pressure in a gas cylinder. Compressed gases are used in medical applications, industrial processing (such as semiconductor processing), and cutting and welding, among others. High-pressure cylinders are used for gas storage and transportation. The two pressure gauges shown here are attached to the cylinder and used for measuring the inlet (upstrem) and the outlet (downstream) pressure. The inlet pressure indicates how much gas is left in the cylinder and the outlet pressure is used to monitor the flow of gas out of the cylinder.