It looks like the author simply linked to the wrong paper. The linked note is The Single Server Queue in Heavy Traffic by Kingman (1960). However, Kingsman's fo

It looks like the author simply linked to the wrong paper. The linked note is The Single Server Queue in Heavy Traffic by Kingman (1960). However, Kingsman's formula was actually defined in On Queues in Heavy Traffic by Kingman (1962)[0]. I cannot find a copy of the latter but based on the preview they appear to be different (but related) works. [0] https://www.jstor.org/stable/2984229 https://www.jstor.org/stable/2984229 [1] https://en.wikipedia.org/wiki/Kingman%27s_formula https://en.wikipedia.org/wiki/Kingman%27s_formula