Control system theory finds widespread applications in several areas of engineering and technology. The developments of state-space transfer function based methods have made it feasible to design a control system for higher-order linear systems. When the order of the system becomes very high, special algebraic techniques for performing the design calculations are required. Moreover, a control system designed for a very higher-order linear system is likely to be more complicated than it would be reasonable to build. The method of dealing with a process of uncomfortably higher-order is to approximate the process by lower-order process, which adequately represents the original model.