Carefully cut around the outside edge of each circle with scissors. Use the point of the scissors or a pencil to make a small hole at the center of each disk. The hole should ONLY be large enough for the fastener to be able to fit the fastener through both disks to hold them together and allow them to turn. If you use a paper fastener, make a small slit in the top disk for the fastener to go through and a regular hole punch in the bottom disk to ensure ease of movement.
To encipher: first select a phrase to supply the key values and share it with any friends to whom you want to send secret messages. The phrase could be a word like "CRYPTO" or any other name or phrase. Next write down the text of your message.Underneath the message, write the key phrase over and over until you have one letter of the key phrase for each letter of your message. Now for each letter of your message that is to be enciphered, find the matching letter of your keyphrase on the small inner wheel and place it under the letter A on the outer wheel. Locate the letter from the message on the outer wheel. The letter on the inner wheel that is under the letter from the message is the ciphertext. In the example shown below, to encrypt the first letter of our message ("I"), we put the C on the inner ring under the A on the outer ring. Then we find I on the outer ring (without moving the disks!) and see that the matching letter on the inner ring is K. For the next letter ("N"), we would move the letter R on the inner ring to under the A on the outer ring and then look for the letter N on the outer ring, reading the inner ring value of E as the cipher text.
To decipher, position the first letter of the key phrase on the inner wheel beneath the letter A on the outer wheel. Find the first letter of the cipher text on the inner wheel and read the letter of the message opposite it on the outer wheel. Repeat for each letter of the cipher text using the letter of the key phrase next after the last one you used until you have recovered the original message.