The automobile industries have seen a great evolution since 19th century. Reducing the NOx emissions from Diesel engines remains as a challenging issue as the emission standards for Diesel engines & its powered vehicles have become more stringent than ever before. As one has to develop for improved life-style, something has to be sacrificed and one among them is global warming. So, many nations have come up with regulations to control exhaust emissions of the vehicles. In the case of Medium & Heavy Duty Diesel Engines, the emissions to be met on Engine Dynamometer on both ESC & ETC cycles for BS-IV or Euro-IV as on date. In which, the optimizing the emission parameters are logically used to meet Random NOx requirements.The calibration technique is to optimize the emission parameters such as Air & EGR Flow-rate, Injection Timing & Quantity and Injection Pressure in logical interpolated manner between the emission mode points (12-modes) of ESC-Emission cycle, the idling mode is excluded. It's done for all quadrants and meeting the calculated random average of any selected Random NOx requirements to pass with good emission margins. The calibration methods and techniques are prepared to meet the requirements of ESC & ETC cycles simultaneously. As the on-road Fuel Economy is the prime requirement for medium & heavy duty diesel engine applications, calibration technique is targeted for best possible BSFC without compromising on Emission with the Random-NOx approach.The optimization & interpolation of emission parameters between the standard 12-mode points give the confidence to meet the random NOx requirements.