Numerals (or figures) can take various forms. The figure style you choose ought to be appropriate to the project you are working on. Readability is key. But which style is best for which purpose? There are two main forms, oldstyle figures (OSF) and lining figures (LF). Each can come in tabular and proportional widths. See some examples above.

Oldstyle Figures

Lining Figures

Lining figures are derived from oldstyle figures. They are a modern style with all figures at a common size and position and even height as the uppercase letters (but sometimes smaller and lighter than the capitals). Today, most fonts use these as default. Lining figures sit on the baseline as opposed to oldstyle figures that appear at different heights and positions. They optically align along a height line and the baseline. The best applications are business reports, forms, tables or any place where alignment is crucial. Lining figures are also known as regular numerals or titling figures.

Tabular Figures

Tabular figures are mono-width, they align vertically and thus appear in documents that compare numerical data in columns. Each figure shares the same width and space on both sides.

Proportional Figures

Proportional figures are different in their total character width. They are spaced to fit together more like letters. For instance, the figure 1 is very narrow like the letter l and takes up less width than the number 6. Because their spacing appears more even, these figures are best in texts and headings where columnar alignment is not necessary.

Now that you know the differences between the two figures styles and their two widths, you know what to buy for your particular needs. Fortunately, some foundries (like FontFont) make it simple: every figure style that has been designed for a particular typeface is included in each purchasable package. OpenType, though, makes it even simpler. Most OpenType fonts include all available figure styles within a single font. So there’s no switching between fonts to get to the right figures. Read more about the conveniences of the format on our new OpenType page.

Source: recovered from FontFeed