As with most elements of professional typography and typesetting, the devil is in the detail. The reader should be oblivious to everything but the narrative of the story, and this includes the appearance of numerals. The choice is non-lining or lining figures within the body of the text.
Non-lining figures, also called lowercase figures, are designed to sit within body copy as they simulate the x-height of the lowercase letters. Not only is the physical proportion of the numeral considered, their design also allows for particular numerals to extend above or below the line, which helps them blend in with the surrounding letters.
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