A spiral spring of 15mm diameter and 10cm long is firmly attached to a rigid clamp of a stand at its upper end with the help of a chucknut. A slotted weight (50*5gm, set) is attached to its lower end. A pointer is fixed in a horizontal position at the lower end of the spring just above the hanger. A half meter scale is fixed vertically in the same stand. It is kept in the front of pointer such that tips of the pointer move just over the scale without touching it. With 50*5gm slotted weight.