One of my sons has signed up with the S.H.O.E. Academy a fun site for espionage fans. One of the regular tasks is to decipher messages using a code wheel
The is made up of two concentric circles each made up the letters of the alphabet with the outer ring in regular order and the inner ring, which you can spin, effectively randomized The challenge for the agent is to find which letter in the inner ring to use to align with the ‘A’ in the outer ring.