Mores Code

In 1836, Samuel Morse demonstrated the ability of a telegraph system to transmit information over wires. The information was sent as a series of electrical signals. Short signals are referred to as dits (represented as dots). Long signals are referred to as dahs (represented as dashes). With the advent of radio communications, an international version of Morse code became widely used.

The most well-known usage of Morse Code (CW) is for sending the distress signal: SOS. The SOS signal is sent as:

Morse code relies on precise intervals of time between dits and dahs, between letters, and between words. Here's a chart that shows these relationships:

The speed of transmitting Morse code is measured in WPM (words per minute). The word "Paris" is used as the standard length of a word. To transmit the word "Paris" requires 50 units of time. If you transmitted the word "Paris" 5 times, you would be transmitting at 5 WPM. An experienced Morse code operator can transmit and receive information at 20-30 WPM.

ARRL

http://www.arrl.org/code-practice-files