Most all materials, if put under a certain stress, will change. In the case of the string in our kit, it will stretch in length, and the amount of stretch depends on the type ofstring, its length, the amount of stress, and its thickness. Set up the stand as shown here. Measure the string without any weight other than the hook. You should also measure the diameter of the string. Then you place a large weight measure the length of the string under this stress