Material required to be classified is charged as thin bed into the upper deck over the screen.Coarser particles remain over screen, while fines pass through the screen and enter into lower deck. Particles over each screen in each deck are discharged automatically from individual discharge spout of each deck. Rotation of top eccentric mass causes vibration in horizontal plane and if it is increased, it will increase horizontal throw on screen will cause the over size material to discharge at faster rate. The lower weight causes vibration in vertical plane and tangential plane. It is desirable to promote maximum vertical vibration in order to dislodge material and to clean the screen. The tangential component of vibration and hence circular motion of particles in the screen are controlled by the angular position of the top and bottom eccentric weights to give better screening efficiency.