Typographic approximation
For a printed medium (such as paper), a typographic approximation is a replacement (approximation) of some element of the writing system (usually, a glyph) with some else glyph(s), such as a nearly homographic character, digraph or character string. An approximation is different from a typographical error in that an approximation tries to preserve visual appearance of a glyph. There are approximation for non-printed visual presentation such as displays. 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 digital 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 shortage in available characters.
| Normative: | 3 × 2 − 1 |
| Approximated: | 3 x 2 - 1 |
| An ASCII approximation of an arithmetical expression | |
Typewriter and line printer approximations
Merger of characters
On typewriter, several characters were merged due to limited size of glyph repertoire. Several modern computing characters appeared by merger of different symbols, such as the "typewriter" apostrophe,', which can denote an apostrophe proper,’, a single quote, and the prime symbol.
Non-spacing modifiers
Some typewriters have non-spacing keys used as diacritical marks. After the typist pushes, say, acute accent ◌́ the caret does not move. This allows the typist to overstrike this mark by a spacing letter, say, e and obtain é, an accented letter. Due to geometrical restrictions of a monospaced font, the result could not always be perfect. For example, overstriking unlikely was a feasible method to produce uppercase accented letters, such as É.
Overstrike was used on line printers for the same goal. This contributed to standardization of such characters as U+0060 ` .
Overstrike was also used to simulate boldface letters with line printers.
ASCII approximations
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| An ASCII approximation (above) may be ugly, but giving some representation of several symbols. Replacements of non-ASCII characters (others than default "*") are highlighted in yellow. | |||||
The US-ASCII character set and other variants of ISO/IEC 646 contains 95 graphic characters. It is comparable with a (Latin script) typewriter and insufficient for a quality typography. But high availability and robustness of ASCII character encoding prompted computer users to invent ASCII substitutes for various glyphs. Following ASCII character are used to approximate:
Also there are many Latin letters, homographic to letters of other scripts; this is not listed. Approximation of non-glyphsThere exist various approximation for typographic alignment. For example, justification may be emulated with inserting of spaces, and flush right alignment may be done by padding with spaces. There are various techniques for approximation of tables (historically used for text mode displays), such as box drawing characters. Modern situationIn digital technologies, there are still some conditions where typographic approximations are appropriate. There are some devices (such as mobile phones) which can not support huge character repertoire and power text formatting tools, which are ubiquitous on desktop computers of the 2000s. References
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