Oscillation, in general, is a periodic fluctuation between two things; in the broadest sense, oscillation can occur in anything from a person's decision-making process to tides and the pendulum of a clock. Oscillation in a device called an oscillator is usually a back and forth motion over a central neutral point, created by changes in energy. In a pendulum-driven clock, for example, the oscillation is the back and forth movement of the pendulum. Oscillators may be mechanical or electronic, but all work on the same principles. Other devices based on the principles of oscillation include the oscillograph and the oscilloscope.