Morse code [for S. F. B. Morse], the arbitrary set of signals used on the telegraph (see code). It may also be used with a flash lamp for visible signaling. The international (or continental) Morse code is a simplified form generally used in radio telegraphy. The American Morse differs from the international Morse in 11 letters, in all the numerals except the numeral 4, and in the punctuation code. The unit of the code is the dot, representing a very brief depression of the telegraph key. The dash represents a depression lasting three times as long as a dot. Between the depressions there is a pause equal in time to one dot, except in a few letters and signs, when there is a wait of two dots. The pause between letters in a word lasts as long as one dash, between words it lasts as long as two dashes. The International Morse code is shown in the table entitled Morse Code. Morse code is now mainly used by amateur (ham) radio operators. The U.S. Coast Guard stopped monitoring Morse code transmissions in 1995 when their use in sending distress calls had been almost entirely superseded by automated systems using satellite relay.