The Fluenta FGM 160 measures gas velocity based on the time–of–flight technique. The ultrasonic transducers are mounted at an angle to the pipe. Both transducers transmit and receive pulses and the transit time is measured. When the gas is flowing in the pipe, the pulses travelling against the flow take longer to reach the opposite transducer than the pulse travelling with the flow. This time difference is used to calculate the velocity of the flowing medium.