letter spacing had to be uniform. In modern digital page-layout software, high-end applications all use relative measurements proportional to the size of the type. QuarkXPress uses units of 1/200 of an em, and Adobe InDesign uses 1/1000 of an em. Therefore, in QuarkXPress, a tracking setting of 3 reduces the visual density of the text noticeably, but in InDesign a tracking setting of 3 is barely noticeable. Fixed spaces Letter spacing may also refer to the insertion of fixed spaces, as was commonly done in hand-set metal type to achieve letter spacing. Fixed spaces vary by size and include hair spaces, thin spaces, word spaces, en-spaces, and em-spaces. An en-space is equal to half the current point size, and an em-space is the same width as the current point size. Changing kerning perception Even with no kerning control, a visually pleasing result can be achieved with some control of the space between letters. With CSS1, a standard of 1996, the property (illustrated) offers some control for "kerning perception", as kerning can be simulated with non-uniform spacing between letters. The CSS3 standard includes the property. In the meantime, web designers used the workaround of , mainly to enhance spaced texts of titles and banners. Legibility Adjusting the letter spacing of a given text has been shown to affect reading speed and accuracy. A wide body of research suggests that text with wider letter spacing, as well as wider line and word spacing, leads to increased reading comprehension among both dyslexic and non-dyslexic children. Contrarily, tighter spacing is thought to decrease comprehension, and is accompanied by crowding and a perception of smallness. Letter spacing adjustments are frequently employed in news design. Due to deadlines, news editors do not usually have time to rewrite paragraphs that end in split words or create widows or orphans. Discussing Comic Sans, some researchers, including Sue Walker, Jenny Thomson, and John Stein, posit that the typeface's wide spacing, rather than the shape of its characters, is the reason for its success among dyslexics. See also Emphasis in typography Kashida Microtypography Sentence spacing Typographic ligature Word spacing Notes References Bringhurst, Robert. The Elements of Typographic Style. Hartley & Marks: 1992. . Kane, John. A type primer. Prentice Hall: 2002. . Lupton, Ellen. Thinking with Type: A Critical Guide for Designers, Writers, Editors, & Students. Princeton Architectural Press: 2007. ). Spiekermann, Erik. Stop Stealing Sheep & Find out how