Font Styles for Numerals
Most modern fonts have numerals that are all the same height as capital letters:
However, some books that we see while proofing may use an older font style in which the height and vertical placement of the numerals vary:
These are often called old-style figures, while the first example shows lining figures. Occasionally a book may even use both styles; for instance, an index might have page numbers in one font style and line numbers in the other.
- Text figures at Wikipedia