Something you may not have noticed when reading your favourite book, magazine, journal or any piece of correctly typeset copy is the style of the numerals used within the text.
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. In contrast, lining figures are uniform of height and width. This makes them stand out within body copy and halt the reader, disturbing the flow of the text and thus adding to the possibility of a less desirable reading experience.
However, lining figures do have an important part to play in typography. In a situation where there is the appearance of all uppercase copy, it would be perfectly fitting to use these figures as they align with the cap-height of the typeface and would blend in well, whereas non-lining figures wouldn?t. This also applies to any situation where numerals appear as stand-alone copy, such as telephone numbers and postcodes.
When considering the typeface for any particular project it always helps to look at the character set of that particular font to determine whether or not it has all the characters you need. This includes, in this instance, the lining and non-lining figures and can also include stylistic alternatives to particular characters or small caps.