I found something similar to the clack towers actually in use in the 19th century. You can vaguely see the next "tower" in the background of the model. Thios particular setting was part of the message "The Duke of X and X has safely arrived home.", and from the few combinations needed to pass the message along, it seems to me that entire words, but at best syllables were coded here. ...from the Museum of Technology in Berlin. Deutsches Technikmuseum Berlin - Telecommunications
