Oldstyle figures

A numeral set is a small alphabet, and like an alphabet it can be drawn tall or short. The default in most fonts is the lining set: every digit the same height, aligned to the capitals, drawn to sit beside MMXXIV without a step in the line. Oldstyle figures are the other drawing. Their bodies sit at the x-height, a few of them rise to the ascender, and the rest drop a tail below the baseline, so a number in the middle of a sentence has the same rhythm of ups and downs as the words around it. The usual pattern is 0, 1 and 2 at x-height, 6 and 8 rising, and 3, 4, 5, 7 and 9 hanging, though the exact set is the type designer’s call.

The reason to reach for them is the same reason a paragraph does not shout. Lining figures are drawn at the cap height, so a date inside running lowercase reads as five capital letters dropped into the sentence, and the eye stops at them. That is a virtue in a price, a total, or an interface number that has to be found at a glance, and a nuisance in a footnote, a citation, or an essay about the eighteen nineties. The same instinct produces small caps: capitals that have to appear inside a sentence get redrawn to lowercase height so they stop interrupting it.

Keep it clear of tabular figures, which answer a different question. Tabular is about width: every numeral given the same advance so that columns of numbers line up digit under digit, whatever the values are. Oldstyle is about height and shape: numerals redrawn to the proportions of lowercase so a number stops standing out in a paragraph. A face can offer either, both, or the two combined, which is why a good text family ships four figure sets, and why “proportional oldstyle” for prose and “tabular lining” for the accounts is a normal pair of choices rather than a contradiction.

In practice the switch is font-variant-numeric: oldstyle-nums, or the onum feature underneath it, and it does nothing at all in a face that carries no oldstyle set. That silence is the trap: the CSS is valid, the build is clean, and the numbers stay lining. The specimen on this page is set in Vollkorn, where the arrangement runs the other way: the oldstyle set is the default and lnum is the switch, which is normal in a book face and worth knowing before you write onum, see nothing change, and conclude the feature is missing. Both heights are ruled across the line there, because a claim about a height is only readable against a line, and the number changes width as it changes drawing: a real oldstyle set brings its own advances.