In Chapter 4, Roger Reedy provides commentary for the understanding and application of the principles of the ASME B&PV Code. Roger traces the history of the Code, from its initial charter and the voluntary effort of engineers for establishing a Code with a safety record to the current Code developed by a consensus process. Roger suggests that Code Users apply common sense when using the Code and for understanding Code requirements. He emphasizes that “the Code is not a handbook and cannot substitute for the use of engineering judgment.” Also, Roger emphasizes the need for a better understanding of the basic principles of the Code Interpretations in the application of safety factors for the Section III Nuclear Code, the Section VIII Pressure Vessels, and the Section I Boiler Code. Roger states that the term safety factor is both incorrect and misleading, because a reduction in the factor seems to indicate a reduction in safety. In fact, when the Code Committee considers a reduction in design factor, it allows the reduction only after it determines that other changes in Code requirements have compensated for the reduction.