Here's a way to send a secret message on a piece of string. First, write the alphabet on a long strip of cardboard as shown. Color one end of the string to show which end starts the message. Put the colored end of the string at the beginning of the scale and tie a knot in a position corresponding to the first letter of your message. For the next letter, put the knot you have just tied at the beginning of the scale and tie the next knot in a position corresponding to the next letter, and so on. (Leave an open square at the beginning of the scale so you'll have room to tie a knot for "A.")