This wearable decoder disk is a gadget every spy-friend should own.
How to use the decoder: The silver alphabet's the everyday one; the red's the code. Use the day of the week to determine where the code begins. If it's Friday, for instance, rotate the inner circle so that the red F is just beneath the silver A; if it's Saturday (or Sunday), move the S below the A, and so on. To encrypt your message, translate from the silver to the red, so that (on Friday at least) ABC becomes FGH. To decode, go from red to silver. And MF?J KZS!
Use a compass and pencil to draw 3 circles on the silver poster board (two 3 1/4 inches across and one 1 1/2 inches across), plus 1 on the red poster board or card stock (2 1/2 inches across). Cut them out with scissors.
Use a ruler and pencil to mark off twenty-seven 3/8-inch increments around the perimeter of a large silver circle.
With a compass point (or scissors), pierce the centers of all of the circles except one of the large silver ones. Attach the red circle and measured silver circle with a paper fastener.
Extend the lines on the silver circle onto the red circle as shown. Use a permanent marker to print the letters of the alphabet around the perimeter of both circles, inserting a question mark between A and Z.
Remove the paper fastener, add the small silver circle on top, then replace the fastener.
Duct-tape the paper clip to the back of the letter N as shown. Use double-sided tape or a glue stick to attach the remaining silver circle to the back of the decoder, then thread the ball chain through the paper clip.