While krypton is generally an inert element, in extreme volatile conditions, it can form compounds in very small quantities. There are several ways that krypton can form its fluoride: by passing through an electrical arc, proton bombardment or photochemical process. All these processes require a very heavy amount of energy. Krypton has achieved a unique importance in science. In 1960, it was decided that the fundamental unit of length, the metre, should be defined in terms of the orange-red spectral line of Krypton 86.