Derating is a versatile technique supported by all static timing analysis (STA) tools in industry. In essence, it enables designers to modify any delay or slew computation performed by such tools. Despite this common use in industry, the scientific literature on derating is scarce to none. This has led to its incorrect use, misunderstanding, and even dismissal. This situation has also been exacerbated with the emergence of statistical STA. This paper is our attempt to fill this void in the literature. We review the use of derating in the context of STA, discuss the important issues, and provide answers to its correct use. We also provide experimental results to justify our claims. Our contribution builds a theoretical and practical foundation to help designers get more insight into derating.