The Folded Book

First fold the strip in half right down the middle. Unfold and then fold the two
sections you just made up to the middle crease. Make all 3 creases into mountain
folds (crease up). Now fold those sections in half again until you have 8 even
sections. You will have 7 creases in which to make into mountains again. Fold
the eight sections in half again, starting with one end and fold all the way through
the accordion. Now you will have 16 even sections. With this technique you will
have an even accordion no matter how long the paper is!"

The Folded Book
by Yasutomo

[Thanks zephyr!]