The pendulum is derived from the plumb line. It consists of a weight suspended from a string fixed at one end, so that the system can be made to oscillate. The oscillations of the pendulum, despite their continuous change in amplitude, are completed in approximately equal times. The duration of a complete oscillation is called the pendulum period; it varies according to the length of the pendulum. Galileo (1564-1642) was the first to establish the isochronism of the pendulum and the laws governing the relationship between the length of the pendulum and the oscillation period. He was also the first to use the pendulum for regulating a clock's escape mechanism.