When a second-order system has ζ ζ < 1 (that is, when the system is underdamped), it has two complex conjugate poles that each have a real part of − − α α ; that is, the decay rate parameter α α represents the rate of exponential decay of the oscillations. A lower damping ratio implies a lower decay rate, and so very underdamped systems oscillate for long times. For example, a high quality tuning fork, which has a very low damping ratio, has an oscillation that lasts a long time, decaying very slowly after being struck by a hammer.