Morse code thus determines the dot length. It is common to assume that a word is 5 characters long. There are two common typical words: "PARIS" and "CODEX". PARIS mimics a word rate that is typical of natural language words and reflects the benefits of Morse code's shorter code durations for common characters such as "e" and "t". CODEX offers a word rate that is typical of 5-letter code groups (sequences of random letters). Using the word PARIS as a standard, the number of dot units is 50 and a simple calculation shows that the dot length at 20 words per minute
American Morse code US needing to be proficient in both codes since messages on transatlantic cables were in the international code, and incoming messages needed to be recoded and sent on in American Morse. An attempt in 1854 to make International Morse the standard within the US was rejected by the telegraph companies. Overhead wires, used for most land routes in the US, have nowhere near as big a problem with dispersion as undersea or underground cables and the companies had no wish to retrain their staff. In the late 1890s, radio communication—initially known as "wireless telegraphy"—was invented, and used Morse Code transmissions.