The singleneedle instrument is a vertical needle galvanoscope worked by a battery and reversing handle, or two " tapper " keys, the motions to right and left of one end of the index corresponding to the dashes and dots of the Morse alphabet.
If this is the case, chances are it will look almost like a high school geometry assignment with grids, lines, dots and angles.
Dots and dashes are distinguished by the interval between the sounds of the instrument in precisely the same way as they are distinguished when reading from the recorder by sound.
A modification (known as the cable code) of the ordinary single needle alphabet is used; that is to say, currents in one direction indicate dots and in the other direction dashes.
The interpretation of the signals is according to the Morse code, - the dot and dash being represented by deflexions of the line of dots to one side or other of the centre line of the paper.
