It is a compound pendulum constructed on the principle that centre of oscillation and centre of suspension are interchangeable. It consists of a steel rod of 120cm long and 1.0 cm dia capable of two adjustable knife edges facing each other. Two metal weights (made of cast iron) of dimension 7.5 × 3.75cm (length × diameter) and (3.5 × 3.75cm) respectively can be made to slide along the length of the bar and can be clamped in any position. Two wooden weights exactly similar to metal weights can also slide along the bar. With the help of this apparatus we can find acceleration due to gravity at a place.