Measurement position. There are several options in selecting measuring position for different-shaped ducts. And such details are specified in available engineering test standards (1, 2, 4,15). The simplest method is to divide the flow area into smaller equal areas, making measurements at the centroid of each small area and assigning the measured velocity to that area. Regardless of the option selected, the average flow rate is estimated along each cross section traversed using Equation 10.2 and the pooled mean of the flow rates for the m cross sections calculated to yield the best estimate the duct flow rate. Uncertainty is assessed both by repeating the measurements and by analyzing for spatial variation effects. Example 10.1 illustrates this method for estimate volume flow rate.