1 6.1 The Quasi-H∞ Smith Predictor 2 6.2 The H2 Optimal Controller and the Smith Predictor 3 6.3 Equivalents of the Optimal Controller 4 6.4 The PID Controller and High-Order Controllers 5 6.5 Choice of Weighting Functions 6 6.6 Simplified Tuning for Quantitative Robustness