The DUL ultrasonic flow meter works according to the delay process. This measuring process is based on a simple physical principle. It is comparable with two canoes crossing a river diagonally – one with the current and one against the current. Naturally the canoe that goes with the current reaches the other side faster than the canoe that is going upstream. Acoustic signals behave in a very similar manner.  The lag times of the signals heading upstream and down- stream are measured using three pairs of patented ultrasonic measuring sensors. The difference in time lag is proportional to the average flow velocity and is converted into an output signal that serves to display the volume flow-through rate and the total flow-through.