The fulcrum of the teeter totter, shown below, can be used to locate the vertical plane through the pivot line of the board. If desired, a piece of tape can be used to indicate this plane when the teeter totter is nearly balanced. Planes can be determined with the subject lying on the board, standing on the board facing forward, and standing on the board facing to the side. The intersection of these three planes is the center of mass of the body.
It is not easy to obtain an exactly balanced position; usually the best that you can do is to oscillate back and forth about the equilibrium point by slight shifts in your position.