The concept of approximation also applies to the World Wide Web and other forms of textual information available via digital media, though usually at the level of characters, not glyphs.
Historically, the main cause of typographic approximation was a low quantity of glyphs (such as letterforms and symbols) available for printing.
In the age of World Wide Web and digital typesetting, especially after the advent of Unicode and enormous amount of computer fonts, typographic approximations are usually caused either by low ability of humans to distinguish and find needed symbols or by inadequate replacement patterns in word processors,[1] rather than by lack of available characters.
On typewriter, several characters were merged due to limited size of glyph repertoire.
There are various techniques for approximation of tables (historically used for text mode displays), such as box-drawing characters.