Braille
As first made by Louis Braille, the first group of characters, using just the top 4 dots of the braille cell, represents letters "a" through "j" (this group of ten characters is called a decade).  Dot 3 (bottom left) is added to each of the "a" through "j" symbols to give letters "k" through "t".  Both of the bottom dots (dots 3 and 6) are added to the first decade to give letters "u", "v", "x", "y", and "z".  The letter "w" is left out of this group because French did not use the letter "w" when Louis Braille made his alphabet.  The fifth decade is the same as the first decade, but shifted down by a row (dots 1 and 4 are blank).