Generally, a pendulum having part of its weight above the point of suspension. The greater the proportion of weight above the suspension, the longer the period of vibration of the compound pendulum. A theoretically perfect pendulum has all the matter composing it at its centre of oscillation. This is, of course, impossible in practice. The pendulum rod, for example, however thin, must have some weight which is not concentrated at the pendulum bob's centre of oscillation. All practical pendulums are partially compound, because the weight of the components cannot by concentrated at the centre of oscillation.