It consists of a heavy cast iron rectangular plate of dimension 15×10×1.5cm. The plate has six holes, two holes on top, two holes on front side and two holes on the third side of the top. The plate is suspended by means of two strings of equal lengths from a rigid support (i.e. a heavy ‘T’ shaped clamp. with two split chucks is provided on the heavy base.) When the plate is suspended freely, the two strings will be equally inclined to the horizontal face of the plate.