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This decoder is used for decoding and coding the caesar cipher. 
http://en.wikipedia.org/wiki/Caesar_cipher
You could make two and give one to your friend so you can send secret messages to each other

Step 1: Materials

Soft drink can
pen
stanley knife
ruler
compass
a paper clip (I forgot to take a picture)
Scissors (optional)

Step 2: Cut Up the Can

Use the stanley knife or scissors to take off both ends of the can. I prefer using the knife to the scissors.

Step 3: Prepare the Can

Cut the cylinder to make a rectangle and flatten it by rolling it backwards 

Step 4: Draw & Cut Out the Parts

Radius of the small circle is 2 cm and radius of the big circle is 3 cm.
Cut them out with a stanley knife or scissors

Step 5: The Maths-Outer Circle

Step 6: The Maths-Inner Circle

This is how to work out how wide each letter should be

Step 7: Draw the Spaces

Use the previous calculations to space each sector. Try to get them as accurate as possible.
Make another circle on the smaller circle with the pen with about a 1 cm radius.

Step 8: Draw on the Letters

Draw on the spaces where the letters will go first

Step 9: Put It Together

Put a paper clip through and bend the ends over it or you could put some hot glue on
you put three pictures there

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