Abstract: A system for measuring the flow of a fluid in a pipe that is one of a plurality of different sizes. The system employs a pair of transducers mounted on the pipe in an upstream-downstream relationship, Each transducer is excited by one of a pair of oscillators to transmit a sonic signal though the fluid to the other transducer. Transit times of the sonic signals are measured. A microprocessing network computes the flow rate of the fluid based on the measured transit time in the pipe. The system has a signal transit time between transducers equal to the time elapse of N cycles of the frequency emitted by the oscillators. The value of N, as computed by a microprocessor, relates to the size of the pipe.