**9. Conclusions**

By the use of LQR theory we formulated a control-tracking problem and showed those cases when their solution gives members of the PImDm-1 family of controllers. This way heuristics are avoided and a systematic approach to explanation for the excellent performance of the PID controllers is given. The well known one block PID controller architecture is optimal for Linear Quadratic Tracking problem of 2nd order systems with no zero or stable zero.

**Part 2** 

**Tuning Criteria** 
