Noise Rating (NR) Curves have been a fundamental tool for assessing building services noise in the UK for several decades. Despite their widespread use, the origins of the NR Curves are not well known. Traditionally, they are defined as a series of linear functions across octave bands, typically derived from a table of coefficients. However, there are inconsistencies and errors in their reproduction, including previous versions of BS 8233. This talk will examine the historica