G by Free fall PSAW To determine the value of G. It consists of an electronic unit having four sockets and a switch to help hold or release the ball. A heavy retort stand carries a solenoid. When toggle switch is on catch position, currents flows through soleniod producing a magnetic field and holding the ball. The retort stand carries another base. The ball after being released from solenoid falls on this base. Time taken by hte ball to travel from solenoid to second base is recorded in electronic unit.