Originally the sizes in the scale were referred to by name instead of by point size. here’s a few examples of some of the older names:
6pt: nonpareil
7pt: minion
8pt: brevier or small text
9pt: bourgeois or galliard
10pt: long primer or garamond
11pt: small pica or philosophy
12pt: pica
14pt: english or augustin
18pt: great primer
21pt: double small pica or double pica
24pt: double pica or two-line pica
36pt: double great primer or 2-line great primer