Manipulating Type Size and Vertical Spacing (The GNU Troff Manual)

### 5.20 Manipulating Type Size and Vertical Spacing

These concepts were introduced in Page Geometry. The height of a font’s tallest glyph is one em, which is equal to the type size in points.82 A vertical spacing of less than 120% of the type size can make a document hard to read. Larger proportions can be useful to spread the text for annotations or proofreader’s marks. By default, GNU `troff` uses 10 point type on 12 point spacing. Typographers call the difference between type size and vertical spacing leading.83