The gauge includes a measurement tube (1) having at least an ultrasonic transmitter which vibrates a medium. The reflected wave is received and detected by an ultrasonic receiver. The reflection area of the tube has such structure on its external wall (13) that the remaining internal wall strength (11) is weak, suppressing a beam offset reflection. The structuring of the outer wall of the tube follows a regular pattern. The structure of the outer wall has holes, sections or uses other material removing methods on the outer wall.
