In the good old days, Kodak used to publish a set of books called Dataguides that had all kinds of useful information. The darkroom dataguides included a “standard” negative and print; the idea was that the user had a practical reference of what a well exposed, well-developed negative and print looked like. He could also use this negative as a standard test to calibrate his own equipment or fine-tune his procedures. (Later Dataguides did not include these, probably as a cost-saving measure. A shame.)
NPR.org. (2014). How Kodak’s Shirley Cards Set Photography’s Skin-Tone Standard. [online] Available at: http://www.npr.org/2014/11/13/363517842/for-decades-kodak-s-shirley-cards-set-photography-s-skin-tone-standard [Accessed 20 Sep. 2017].