One toot represents 1, two short toots 2, and a long blast the end of a word.

In a fog, this is the only means practicable.

Similar sounds can be made by horn or gunfire.

At night searchlights are often used by waving the beam from the right to the left, thus forming an electric wigwag, or by flash like the heliograph.

On small ships not fitted up with the Ardois system, the Very night signal is used.