Braille

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Braille is a tactile writing system used by blind people. It was invented by Louis Braille of France who was blinded in a childhood accident. At the age of 15 he invented a code based on a military system for reading orders at night without showing any light. Braille originally lacked an encoding for the letter W.

Braille is also notable for being a binary code that predated the invention of the computer.

Braille generally consists of of cells of 6 raised dots conventionally numbered

 1 4
 2 5
 3 6

and the presence or absence of dots gives the coding for the symbol. English braille codes the letters and punctuation, and some double letter signs and word signs directly, but capitalisation and numbers are dealt with by using a prefix symbol.

There are braille codes for representing shorthand (produced on a machine which embosses a paper tape) and for representing mathematics and musical notation.

Braille has been extended to an 8 dot code so that the case of an individual letter is directly coded in that cell, and so that all the printable ASCII characters can be represented. All 256 possible combinations of 8 dots are encoded by the Unicode standard.

Braille may be produced using a "slate" and a "style" in which each dot is created from the back of the page, writing in mirror image, by hand, or it may be produced on a braille typewriter or "brailler", or produced by a Braille Embosser attached to a computer. It may also be rendered using a refreshable braille display.

A0   B1   C2   D3   E4   F5   G6   H7   I8   J9
X.   X.   XX   XX   X.   XX   XX   X.   .X   .X
..   X.   ..   ..   .X   X.   XX   XX   X.   XX
..   ..   ..   ..   ..   ..   ..   ..   ..   ..
K    L    M    N    O    P    Q    R    S    T
X.   X.   XX   XX   X.   XX   XX   X.   .X   .X
..   X.   ..   .X   .X   X.   XX   XX   X.   XX
X.   X.   X.   X.   X.   X.   X.   X.   X.   X.
U    V    W    X    Y    Z
X.   X.   .X   XX   XX   X.
..   X.   XX   ..   .X   .X
XX   XX   .X   XX   XX   XX
Capital   Number                       Question
sign      sign      Period    Comma    mark
..        .X        ..        ..       ..
..        .X        XX        X.       X.
.X        XX        .X        ..       XX
          Exclam.   Opening   Closing
Semicolon point     quote     quote    Bracket  Hyphen
..        ..        ..        ..       ..       ..
X.        XX        X.        .X       XX       ..
X.        X.        XX        XX       XX       XX

Next time you're in an elevator, check the braille:

.X XX
.X X.
XX ..

... means this is the button for the fifth floor (number sign + F).