The traditional method is to use pitot-static tube method. In this, individual velocity is computed for each pressure values and then it is averaged. When the value is averaged and converted to velocity, there is high chance that it will give incorrect result mainly if values are away from average pressure. So, to overcome this, velocity traverses are used to determine air flow rates in duct. In this, duct is divided into concentric circles of same area. Then, equal number of readings are taken to get best possible average value. Same can be done in case of rectangular duct. For accurate values, the traverse specification approved copy should be taken from regulatory body.