For static balancing applications, Ruskin's Model VFBD25 ValueFlo Balancing Damper is well suited for ease of installation and labor savings. Double butterfly type blade arrangements provide smooth air flow and integral air flow measuring ports. Each damper is clearly labeled with its own P.A.M.S. (Pressure Across the Monitoring Device) chart, which coincides with the specified blade angle. So balancing is made much easier and Ruskin qualified the flow rates