It is differential pressure type of flow meter, exactly reverse of rotameter. It is the most widely applied flow rate measuring device for fluid flows in pipes that require accurate measurement. Differential pressure flow meters have a change in flow cross section that can be described as a restriction placed in the flow line that causes the velocity of the flowing fluid to change. The difference in pressures between the two measurement locations of the flow meter is the result of the change in the flow velocities. The volume flow rate through the cross-sectional area is given by