Most people have chakra that has an affinity to one of the Five Elements Nature Transformations. To find out what affinity someone has, pieces of paper that are made from a special type of tree are used to react to the slightest hint of chakra in any number of ways, depending on the nature latent in the chakra.
The chakra paper reactions are as follows:
Fire: The paper will catch on fire and turn into ash.
Wind: The paper will split in half.
Lightning: The paper will wrinkle.
Earth: The paper will turn to dirt and crumble away.
Water: The paper will become damp.