Letter frequency xz. Modern International Morse code (generally believed to have been developed by Alfred Vail based on English-language letter frequencies of the 1830s) encodes the most frequent letters with the shortest symbols; arranging the Morse alphabet into groups of letters that require equal amounts of time to transmit, and then sorting these groups in increasing order, yields e it san hurdm wgvlfbk opxcz jyq. Similar ideas are used in modern data-compression techniques such as Huffman coding. Letter frequency was used by other telegraph systems, such as the Murray Code. Letter frequencies, like word frequencies, tend to vary, both by writer and
Morse code are used to indicate changes in communications protocol status or white space text formatting actions. The symbols !, $ and & are not defined inside the ITU recommendation on Morse code, but conventions for them exist. The @ symbol was formally added in 2004. There is no standard representation for the exclamation mark (!), although the KW digraph () was proposed in the 1980s by the Heathkit Company (a vendor of assembly kits for amateur radio equipment). While Morse code translation software prefers the Heathkit version, on-air use is not yet universal as some amateur radio operators in North America