Abstract: In a device for accurately measuring the dimensions of metallic tubes and the like by supersonic waves in a liquid medium, typically water, obstructions providing reflecting boundaries that are partially reflecting and partially transparent for acoustic waves are provided at different distances from the transmitter-receiver between the latter and the object being measured and echoes of transmitted pulses from the reflecting boundaries of the obstructions and from those of the object being measured are processed in order to obtain the measured dimensions in a manner unaffected by changes in the velocity of propagation of the waves in the liquid medium because of temperature effects and the like. The pulse processing involves obtaining electrical signals proportional to the time delay between pairs of pulses and then comparing the time delays relating to precisely known distances with time delays relating to distances being measured.