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Scytale

A rod, a strip of paper, and the oldest code machine there is.

about 10 minutes easiest one here makes a working machine

What you need

A round rod: a pencil, a broom handle, a rolling pin
A long strip of paper about 2 cm wide
Sticky tape
A pen

How to build it

Cut your stripLong and thin. Two centimetres wide is about right, and as long as you can manage.
Tape one end to the rodThen wind the strip round in a spiral so the edges touch but do not overlap.
Write along the rodNot round it. Write your message down the length, one letter per turn of paper.
Unwind itThe letters are now scattered along a meaningless strip.
Send the strip onlyNever the rod. Your friend needs a rod of exactly the same thickness.
A different thickness of rod gives a different answer. Agree on the object first: both use a pencil, or both use a broom handle.

The template

Print this at 100 per cent, not fit to page, or the sizes will be wrong. The ruler line below tells you whether it printed correctly.

10 cmcut along the long edges, then wind the strip round your rod
The bar above should measure exactly 10 centimetres. If it does not, your printer has shrunk the page.

Now send something

Write MEET ME BY THE GATE AT FOUR. Unwind it, look at the nonsense you are holding, then wind it back on and watch it come together.

The rail fenceBack to Make

Read more elsewhere

Longer, harder and written for grown-ups. Worth a look when this page runs out.

Scytale