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
Morse code abbreviations the same as the prosign for "end of telegram", and the widely used but non-ITU "Over to you only" prosign is the official code for open parenthesis [(] or "left bracket". The listener is required to distinguish the meaning by context. In the example casual conversation between two station operators, above, the Morse transmissions in the grey boxes show the equal sign [=] in the same way that a simple electronic automatic Morse code reader with a one- or two-line display does: It can't distinguish context so it always displays the math symbol. It would also display an open parentheses