Typographic approximation

For a printed media (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^{[disambiguation needed]} 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:	$3 \times 2 - 1$
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 pushing, say, acute accent ◌́ the caret does not move. This makes convenient 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 ` GRAVE ACCENT.

Overstrike was also used to make an appearance of boldface letters with line printers.

ASCII approximations

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.

Original text:

                   ASCII*Decima

ASC Dec Hex Binary  
╔═╤════════════════ 
║ │  0  00 00000000 
║☺│  1  01 00000001 
║☻│  2  02 00000010 
║♥│  3  03 00000011 
║♦│  4  04 00000100 
║♣│  5  05 00000101 
║♠│  6  06 00000110 
║•│  7  07 00000111 
║◘│  8  08 00001000 
║∘│  9  09 00001001 
║◙│ 10  0a 00001010 
║♂│ 11  0b 00001011

ASC Dec Hex
╔═╤════════
║►│ 16  10 
║◄│ 17  11 
║↕│ 18  12 
║‼│ 19  13 
║¶│ 20  14 
║§│ 21  15 
║▬│ 22  16 
║↨│ 23  17 
║↑│ 24  18 
║↓│ 25  19 
║→│ 26  1a 
║←│ 27  1b

║─│196  c4 11000100 
║═│205 cd 11001101

║││179  b3 
║║│186  ba

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:

U+0020 SPACE (space): alignment and justification.
U+0022 " QUOTATION MARK: various type of double quotes, double prime ″.
U+0023 # NUMBER SIGN: sharp symbol ♯.
U+0027 ' APOSTROPHE: various type of single quotes, apostrophe ’, prime ′.
Parentheses U+0028 ( LEFT PARENTHESIS U+0029 ) RIGHT PARENTHESIS: encircled characters, such as (c) for Copyright symbol ©.
U+002A * ASTERISK – see Asterisk.
U+002B + PLUS SIGN – various symbols with strokes extending to left, up, right and down.
U+002D - HYPHEN-MINUS – probably an ASCII character the most used for approximations. A conventional representation of hyphen, an approximation of dash (especially as -- and ---), minus sign − and line drawing horizontal line ─ (see the image).
U+002E . FULL STOP: various dot-like symbols, see Full stop.
U+002F / SOLIDUS – see Slash (punctuation).
U+0031 1 DIGIT ONE: Turkish dotless ı, Cyrillic palochka Ӏ.
U+0033 3 DIGIT THREE: IPA reversed epsilon ɜ, Cyrillic letter З.
U+0034 4 DIGIT FOUR: Cyrillic letter Ч.
U+0038 8 DIGIT EIGHT: various non-Latin letters and symbols with similar grapheme.
U+003A : COLON – see Colon (punctuation).
U+003C < LESS-THAN SIGN and U+003E > GREATER-THAN SIGN: chevrons ⟨ ⟩, angle quotes ‹ ›, horizontal arrows (especially as digraphs <- and ->).
U+003D = EQUALS SIGN: line drawing horizontal double line ═ (see the image), double hyphen.
U+003F ? QUESTION MARK – although not an approximation, the question sign sometimes replaces unrepresented and unrecognized characters.
U+0040 @ COMMERCIAL AT – see At sign.
U+004E N LATIN CAPITAL LETTER N: Numero sign №.
U+0054 T LATIN CAPITAL LETTER T: various symbols with strokes extending to left, right and down, but not up.
U+0055 U LATIN CAPITAL LETTER U: set union ∪.
U+0056 V LATIN CAPITAL LETTER V: ∨.
U+0058 X LATIN CAPITAL LETTER X: X mark ✗.
U+005B [ LEFT SQUARE BRACKET and U+005D ] RIGHT SQUARE BRACKET: checkbox and similar rectangular pictograms.
U+005E ^ CIRCUMFLEX ACCENT: ∧, upwards arrow ↑, and similar symbols with the wedge at the top.
U+005F _ LOW LINE – see Underscore.
U+0060 ` GRAVE ACCENT – opening single quote ‘.
U+006F o LATIN SMALL LETTER O: bullets and various circle-like symbols such as ∘.
U+0076 v LATIN SMALL LETTER V: downwards arrow ↓, and similar symbols with the wedge at the bottom.
U+0078 x LATIN SMALL LETTER X: multiplication sign ×.
U+007C | VERTICAL LINE (on the image, this ASCII character is rendered as a broken bar ¦): line drawing vertical symbols.
U+007E ~ TILDE – see Tilde.

Also there are many Latin letters, homographic to letters of other scripts; this is not listed.

Approximation of non-glyphs

There 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 situation

In 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 2000s.

References

^ Phin, Christopher (2008-03-29). "Ten typographic mistakes everyone makes". Retrieved February 15, 2012.

[1] Phin, Christopher (2008-03-29). "Ten typographic mistakes everyone makes". Retrieved February 15, 2012.

[1]