Braille was developed by Louis Braille
in the beginning of the 19th century. 6 dot Braille letters, common punctuation
marks, and a few symbols are displayed as raised 6 dot Braille cell patterns
read by using a fingertip to feel the raised dots. The 6 dot Braille alphabet,
the method for representing Braille numbers, and some Braille punctuation marks
are used in all languages that share the Roman alphabet. There are variations of
6 dot Braille in various Roman alphabet languages. Representation of punctuation
marks and differences in the meanings of other 6 dot Braille cells are commonly
used to represent special characters and/or common letter combinations.
Braille characters are based on a 6 dot Braille cell having two parallel columns
of three dots each. If the empty cell is counted, 64 unique dot combinations are
possible with a 6 dot Braille cell. Dot height is approximately 0.02 inches (0.5
mm); the horizontal and vertical spacing between dot centers within a Braille
cell is approximately 0.1 inches (2.5 mm); the blank space between dots on
adjacent cells is approximately 0.15 inches (3.75 mm) horizontally and 0.2
inches (5.0 mm) vertically. A standard Braille page is 11 by 11 inches and
typically has a maximum of 40 to 42 Braille cells per line and 25 lines.
6-dot Braille
Numbering
1 o o 4
2 o o 5
3 o o 6
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Old 8-dot Braille
Numbering
1 o o 4
2 o o 5
3 o o 6
7 o o 8
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Unified Braille Code
Numbering
4 o o 5
3 o o 6
2 o o 7
1 o o 8
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Unified 8 dot Braille Code 
