An air flow meter is a device used to measure the rate of air flow in a system. It is used to measure the amount of air entering or exiting a system, such as an engine, and is used to monitor and control the air/fuel ratio in the system. Air flow meters come in many different types, including mass air flow meters, differential pressure meters, and thermal mass flow meters. Mass air flow meters measure the mass of air entering the system, while differential pressure meters measure the pressure difference between two points in the system. Thermal mass flow meters measure the temperature of the air entering the system and use this to calculate the air flow rate. All types of air flow meters are used to measure the amount of air entering or exiting a system, and are used to ensure that the air/fuel ratio is optimal for the system.