Abstract: The paper presents a method making a comparison of acoustic results on schools through the use of omnidirectional sonar (possible). The weakness of such sonar for fisheries acoustics is that there is no practical way to accurately calibrate them, due to the fact that they are not designed specifically for scientific research. The procedure employed is through the use in the field of a reference target allowing to compare the echoes from one beam to the other and to evaluate roughly the operational threshold for school identification. Some results from a calibration achieved on a SIMRAD SR240 in Venezuela, 1998, are detailed.